Monday, July 17, 2017

Climbing Through the Ages

Climbing, by thieves and non-thieves, possibly with rope assistance, is a common dungeon, cave, and wilderness activity for explorers. It’s also one of those mundane, real-life skills that I would expect we could “dial in” correctly to our gaming ruleset. Coincidentally, just a day or two after our Rappan Athuk game, my friend Duncan posted a video of himself climbing a free-hanging rope for about 20’ in a gym, which looked pretty impressive to me. Discussion follows:

Indeed. Taking inspiration from the many climbing challenges last week, I felt obligated to investigate the rules present in classic D&D.


Chainmail (1971) mentions the use of ladders in the Siege rules (which are at man-to-man scale) -- 3 men can climb a ladder per turn (1 minute); defender above always gets first strike (p. 23, 25). The only direct mention of climbing in the D&D LBBs (1974) is that swimmers may climb the side of a ship to board (Vol-3, p. 31). Of the first pit trap, it is said, “it would only mean about one turn of time to clamber out, providing the character had spikes or associates to pull him out, and providing the pit wasn't one with a snap-shut door and the victim was alone.” (Vol-3, p. 5).

Of course, Sup-I (1976) introduces the Thief class with their special ability to “climb nearly sheer surfaces, upwards or downwards” (p. 4). The mechanic couldn’t be simpler: “There is a basic chance of 13% that a 1st level thief will slip and fall in climbing. With each higher level attained by the thief this chance is reduced by 1%”. As a formula, that is: 14% – L chance of slipping. Note what is not addressed: time, distance, speed, encumbrance, ability scores, or how many checks are required for a long climb.

AD&D Core Rules

Again, in the core rulebooks, only thieves climbing vertical surfaces is addressed. The probability is similar to OD&D, with an 85% chance of success at 1st level, a 99% at 10th, and so forth (AD&D PHB, 1978). Racial type may modify this; while Dexterity modifies most other Thief abilities, it does not do so for climbing.

The extra/errata notes in the DMG (1979) give movement and surface details for the first time (p. 19). In particular: “SLIGHTLY SLIPPERY surfaces DOUBLE chances of slipping and falling. SLIPPERY surfaces make chances of slipping and falling TEN TIMES more likely.” One interesting thing is how this mechanic makes the most sense in the context of OD&D, where percentages were given in chances to fail (see prior section); but it’s more confusing math when the percentages have been converted to a chance to succeed in the AD&D PHB (last paragraph). For example: 100% – 2 × (100% – P) for a slightly slippery surface, where P is the base chance of success. Like many AD&D rules, this was long a source of confusion to me, until I read OD&D which clarifies the conrext in which the rule was first written. And I think of this as one of many examples that to Gygax, the game was all one continuous work and not discrete, separate editions.

This latter rule is in fact exacerbated in that further down that page it is written, “Most dungeon walls will fall into the fairly rough to rough category. Some will be non-slippery, but most will be slightly slippery due to dampness and slime growth.” That is: Applied strictly, the default chance of falling is twice that apparent to players from reading the PHB.

And there’s yet another subtle-but-significant rule change between the PHB and DMG and that is: the time scale and number of rolls involved in one climb. The PHB asserts that only one roll need to be made for any climb: “It is assumed that the thief is successful until the mid point of the climb. At that point the dice are rolled to determine continued success. A score in excess of the adjusted base chance indicates the thief has slipped and fallen.” But the DMG gives a chart of move rates in “FEET PER ROUND”, in units of either 0, 3, 6, 9, 12, 18, or 24 feet per round; and then it specifies, “Be certain to check each round of vertical or horizontal movement for chance of slipping and falling”. So this page of the DMG has made climbing massively more dangerous to thieves, both generally doubling the chance to fall, and moving from a single such roll per climb to likely many.


For climbing by non-thieves, we’ll need to look outside the core rules by Gygax. For example, such rules appear in the AD&D Dungeoneer’s Survival Guide (1986). While this is past the time when Gygax departed TSR, the author Doug Niles gets instant credibility from me because of his excellent design work in the miniatures rules for AD&D Battlesystem and Star Frontiers: Knight Hawks. Like much of the book, the rules are somewhat too expansive to discuss here in full (p. 14-19), but an overview can be given.

Sheer surfaces like those detailed for thieves in the DMG simply cannot be climbed by non-thieves (p. 14). Compared to thieves, non-thieves are given a base climb chance of 40%, but this can only be applied to easier categories of climb like, “Rough, ledges... pole... tree... sloping wall... rope and wall” (p. 14-15). Bonuses per category apply, between +20% and +40%, making any of these climbs automatic for thieves. Abilities and encumbrance are not considered, but armor is: –5% for padded/studded, –15% for chain/splint/scale/banded, and complete prohibition for any characters in plate mail (p. 16). An even easier mechanic is given for characters rappelling downwards with a rope; +50% modifier and increased speed (p. 17).

Now, the movement rates are again given in units of feet-per-round, so in this aspect the DSG work looks continuous with the rule given in the DMG. However, there is a possibly subtle wrinkle to this; Niles writes, “When a non-thief character begins a climb, he must make a successful Climbing Check roll on 1d100... If a Climbing Check fails, the character can never climb that wall.” Now, read closely, this has the appearance of switching back to only one check per climb (due to the “begins a climb” language), and not rolling round-by-round as per the DMG. That makes climbing safer, although we might wonder about the last part of the rule, esp. for downward-direction climbs (maybe the most common usage in standard dungeon designs?). What happens when a character goes over the edge of a cliff on a rope and fails their check – are they just stuck there helplessly?

Consider the chart above which summarizes different types of characters climbing a rope-and-wall for 100 feet. (The percentages shown would be identical at any level.) Clearly there is a degradation in climbing chances, mostly related to the armor worn by the character. The roll indicated would only be made once; if successful, time spent climbing would be either 3 or 5 rounds by class (where allegedly 1 round = 1 minute).

B/X Rules

In the Moldvay/Cook B/X rules (1981), only climbing rules for thieves are addressed. The chance to climb is actually identical to that back in OD&D (only translated from chance-to-fail to an equivalent chance-to-succeed). The rule stipulates, “This roll should only be made once per 100’ of climb attempted. If failed, the fall will be from halfway up the surface.” (p. B8). So: Here we again see a once-per-climb mechanic (as opposed to the AD&D DMG).

Edit: Scott Keeney points out that Moldvay does briefly mention climbing for non-thieves in his two pages of "Dungeon Mastering as a Fine Art" advice at the very end of the book (p. B60-61). In this case, it's "To perform a difficult task (such as climbing a rope or thinking of a forgotten clue), the player should roll the ability score or less on 1d20." Cook backs this up with a paragraph on Climbing in the Expert rules, suggesting a Dexterity-based check when "climbing a tree in a high wind, or climbing up a crumbling wall." (p. X51)


The subject of climbing is the very last topic in my copy of the AD&D 2E PHB (1989), just before the appendices. Broadly speaking, the rules are the same as those found in the DSG. Base success chance is again 40% for non-thieves; climbing categories are roughly the same; modifiers are slightly adjusted (e.g., +55% for rope and wall); modifiers for armor are mostly the same (exception: plate at –50%, not totally prohibited); checks are again only once at the start of a climb; the rule for quick rappelling downward is maintained; climbing is permanently barred if a character misses their roll. Modifiers for encumbrance rating are added. And another paragraph has been inserted after the table for climbing chances: “On particularly long climbs--those greater than 100 feet or requiring more than one turn (10 minutes) of climbing time--the DM may require additional checks. The frequency of these checks is for the DM to decide. Characters who fail a check could fall a very long way, so it is wise to carry ropes and tools.” (Note that Dave “Zeb” Cook was the listed author for both 2E and the D&D Expert rules, so the echo of the 100’ unit from B/X should not be too surprising.)

In summary, it looks like climbing for non-thieves got significantly more generous than in the 1E DSG. Combined with the boosts to both the rope-in-wall case that we’re considering, and the improved situation for plate, fighter in plate armor have gone from an impossible situation to an almost 50% chance to make such a climb.

D&D 3E

Now, in the 3rd Edition PHB (2000), the formerly percentage-based rules, along with everything else, were converted to the d20-based uniform mechanic. Use of the Climb Skill (p. 64-65) is uniform for all character classes; it’s a class skill and so easily obtained by both Thief-types and Fighter-types (in fact, it’s the very first skill suggested for Fighters in their “starting package”, p. 37); so these classes might be expected to have skill points up to their level + 3 (the maximum). The skill is modified by Strength and Armor (e.g., –1 for studded leather, –5 for chain, –7 for half-plate), but not by encumbrance generally. The d20 target challenge ratings are, for example: DC 5 for a rope and wall; DC 10 for ledges; DC 15 for very rough natural rock or a tree; DC 20 for typical dungeon wall; DC 25 for overhang. DC is +5 for a slippery surface. Many modifiers are given for other situations and synergies. So it looks like, very roughly speaking, the categories of surface are approximately analogous to those first seen in the AD&D DSG.

But one aspect the re-emerges is significant: Rolls must again be made every round. “With each successful Climb check you can advance up, down, or across a slope or a wall or other steep incline (or even a ceiling with handholds) one-half your speed as miscellaneous full-round action.” In conjunction with this, a unique mechanic is that failures are not necessarily falls: “A failed Climb check means that you make no progress, and a check that fails by 5 or more means that you fall from whatever height you have already attained.”

The rule for rapid and easy downward rappelling is missing. But, a rule is added for something that I do think was overlooked in any prior editions: “Someone using a rope can haul a character upward (or lower the character) through sheer strength. Use double your maximum load... to determine how much a character can lift.”

Compare the case-study chart above to those given previously. Although the 3E requests that a check made each round of climbing (counter to the prior case studies), it is in other ways much more generous than in the DSG or even 2E. The modifiers for encumbrance are gone; the effects of armor are more significantly lessened (effectively only a –35% for plate); classes such as fighters as likely to have additional points in the skill; Strength bonuses can apply; and there is no prohibition against re-trying after the first failure. For example, Fighters in plate (–7 check) have that penalty exactly cancelled out by the 4th level (+7 skill); so while they need to roll DC 5 on a raw d20 to succeed in any round, it is impossible for them to fail by 5 and thus fall. They are in fact guaranteed success at climbing a 100' rope in about 1 minute of time (on average around 12 rounds, accounting for failed rolls; and note that 1 round = 6 seconds here).

This is, of course, the furthest possible cry from the 1E DSG where such a climb was strictly prohibited. But if a character is of lower level, or does not have maximum possible ranks in the Climb skill, then the chance of success will be lower -- and due to the multiplication rule for compound probabilities, the total chance to make the climb without a fall degenerates at a shocking rate. For example: At only one level lower (3rd), the fighter in plate will have a 5% less chance to make any particular climb roll (1 pip in 20). But then that opens up the possibility for a fall (on a natural "1"), and over the 10 Climb checks necessary in the example above, the chance for succeeding at the whole climb is only 52.4%. For a 1st level fighter with max skill the total chance is just 12.5%; and for an unskilled climber in plate, the chance becomes less than 1%! (Assuming no Strength bonus, which would move the example back in the other direction.) 1

Poll Results

I also asked this question on the Facebook 1E AD&D group. The results were approximately 3:2 in preference of a check every round (i.e., following the official 1E DMG rule), with another group answering some form of "it depends" (often by distance or surface type).

For what it's worth, everyone whom I know personally picked "one check per climb" (offering a good case study in how your friends can be non-representational of the population at large). EGG Jr. selected "one check per round".

Open Questions

I think that the last time I edited my OED house rules on the subject, I was primarily looking at the 3E rule for base probabilities; however; on my simplified d6 mechanic, making the climb more difficult (as in 1E) would be pretty much countered by the chance-to-fail-but-not-fall (in 3E), for about the same result.

So: Which of the above rules for climbing do you like the best? How risky should climbing be for an unskilled man, a fighter in plate mail, etc.? Do you prefer the frequency of checks to be once per climb (OD&D, B/X, 1E PHB, DSG, 2E), or once per round (1E DMG, 3E)? Should failed checks prohibit any further climbing (as in DSG, 2E), or not? What would be the best simulation of the real thing?

Finally: Anyone ever see anyone test climbing (rope, rock wall, etc.) in any kind of chain or plate armor?

1 This calculation is done by recognizing that the 4-pip window on the check in which no movement or fall occurs can be effectively ignored for this purpose, and proportionally consider the chance to fall out of 16 (with any negative modifier taken as the numerator). Thus, the chance for the 3rd level fighter in plate to avoid any fall is (1 – 1/16)^10 = 0.524; at 1st level it's (1 – 3/16)^10 =0.125; unskilled it's (1 – 7/16)^10 = 0.003. Also checked by computer simulation.


  1. This would seem to indicate that yes, climbing on plate is possible:

    Personally I hate multiplication of probability, because of how shockingly fast it drops off. I prefer one test per climb, though 1 per hundred feet is not too bad a compromise for taking into account really long fatiguing climbs.

    1. Note: Always remember to remove the gauntlets and sabatons when climbing...

    2. Sabatons typically wouldn't be part of plate mail... only really full plate armor and possibly field plate, if you're using the new armors added in AD&D Unearthed Arcana. As for gauntlets, remember that only the top of the hand is armored - the palm side would just be a leather glove/mitten.

    3. The video also includes a helpful link to an actual study of motion in armor.

    4. It's a great video, and I'd seen it before. The wall-climbing is helpful, but I really wish there was a climbing-free-rope example (either successful or failed). Thanks to faoladh for pointing out the academic article, which I would have missed -- I'll plan to read that later.

  2. Here a firefighter (28.5kg enc.) and a soldier (31.2kg enc.) and a knight (29kg enc.) all run the same obstacle course. Maddeningly, the final rope climb of the course is simply not considered part of the course.

    It does suggest that we need not find a video of a knight climbing a rope but rather we accept a video of a firgefighter climbing a rope as an acceptable equivalent.

    1. That was so awesome, thanks for that! I wonder if skipping the rope argues that it wouldn't be possible with that much weight (or else, worry about the mat being damaged). Also it looks like the obstacle two stages earlier was simplified as well (with the four increasing ∩-shaped things; looks like the FF barely got over the first two, so they had them run under the last two).

  3. I am starting to think that a new set of rules should be made and it must take into account the many factors in climbing (direction, equipment, what is being climbed, etc).

  4. I am inclined towards some base roll modified by difficulty and encumbrance per x feet.
    So say 4-6 chance base, minus a pip for light and heavy encumbrance (half stone/full stone), plus/minus a pip for factors like, slippery, bad rope, knotted rope, thief help, per 50'.
    If Champion Goodbody is strong enough to shimmy up a knotted rope in plate, so be it.

    1. That's pretty much what I'm doing at the moment myself. I made the increment every 30 feet in my house rules as of last week.

  5. Love these "game mechanic archaeology" posts. Very helpful for informing my own modifications to the system. I like the idea of a base climbing rule that applies to everyone, with thieves getting some sort of bonus, but I am - at current - agnostic as to how this rule should work.

  6. Apropos of... well, not NOTHING, but only slightly related to this, I am gearing up to make a "final form" version of my own fantasy gaming rules, and I think a good starting point would be to comb through the books and make a checklist of things that I need to decide on rules for, then triage that list by importance and centrality to the system. Did you make such a list when preparing your version of the game, or did you handle it sort of as things came to you?

    1. Yeah, pretty much any time something comes up as awkward or disputatious in a game (or: coding a quantitative simulation and I realize the rule is ambiguous), afterward I go and do a longitudinal study of approaches through the editions and try to make a "best practice" decision (much as you're trying to do). I just recently separated out my "player's house rules" (for character design, which is now pretty stable) and "judge's house rules" (for everything else, which remains in flux for reasons like this).

  7. First, just want to say, I always appreciate these posts of yours, and I really enjoyed the play reports posts as well. Thanks for posting.

    Moldvay did provide BX w/ a rule for non-Thief climbing. It’s presented as an ability check on page B60 (which makes it memorable for me). Again it seems to be a once-per-climb check, though I’d assume the 100-foot distance applies. Here is the relevant text:

    “ ‘There's always a chance.’ The DM may want to base a character's chance of doing something on his or her ability scores (Strength, Dexterity, and so forth). To perform a difficult task (such as climbing up a rope or thinking of a forgotten clue), the player should roll the ability score or less on 1d20. The DM may give a bonus or penalty to the roll, depending on the difficulty of the action (–4 for a simple task to +4 for a difficult one). A roll of 1 should always succeed, and a roll of 20 should always fail.”

    For an ability-based climbing check like that, I’d probably average out Str and Dex and maybe apply Con bonus.

    1. So on X51, Cook clarifies Dex as the BX ability to use for climbing checks.

      To answer your poll question: One check per climb (unless circumstances demand otherwise).

      Having a little danger on all climbs, even those with ropes, is cool, but “too much of a good thing” and all that.

      For most task resolution now I just estimate the difficulty and roll 2d6.

    2. Thanks for the citation to p. B60! Those are interesting pages (last two pages before appendices) -- it's like Moldvay's own personal errata on D&D rules. I tend to forget that content, e.g., the miniature & 1" = 5 ft playing surface rules, but they're really precious insights.

  8. Scott beat me to the punch with the B/X info (I've been busy lately). Back when I ran a regular AD&D campaign, I'm almost certain there were times I made multiple checks. But I wouldn't do that now. No way! Except in combat (where each round of action is important), I try to maintain a "one roll per task" standard.

    1. Appreciated, I always forget about those key last pages in Moldvay!

  9. I favor one check per 100 ft under normal conditions and one check per 50 ft under less than normal conditions.

  10. Love these posts, but some harsh language on D&D climbing rules to follow. None of the D&D rules come anywhere close to a sense of verisimilitude.

    In fact, according to the rules I and everyone I ever knew who free climbed must be like a level 50 thief, and this at the age of 20 with literally 20 minutes of instruction, or we'd be dead...never would have made the rolls otherwise.

    I believe the rules are best based of a real-world climbing scale, see, e.g.,

    Best to base climbing off of DEX and STR (a huge part of climbing is your upper body strength to weight ratio when things get tough, though you do climb with your legs upper body strength allows you to get up to your next set of holds). Another huge part is how flexible you are and if you can well control your center of mass.

    It's both DEX and relative STR (to body mass).

    I'd say all classes can climb anything but the toughest grades without penalty, which thieves can attempt without penalty.

    Different grades requiring a different base DEX and or STR to climb without rolling to see if you fall. If you meet the minimum, you can climb it.

    I would use Thief level as an effective + to DEX or STR when climbing.

    Things that hinder, clothes, armor etc. would a minus to your STR or DEX, a big one. Perhaps the Thief gets no negative modifier for appropriate armor as part of thief training. Slippery surface should increase the grade.

    A slippery rock surface is near impossible to climb unless your holds are more the a fingertip deep (even then). Edging and friction don't work. Chalk does make a big difference.

    1. That's great feedback, and I love hearing from someone with first-hand experience. I totally look at the article on climbing grades in the past, and actually considered using the Welzenbach or French 1-6 scales as the base target on d6 for success (in fact, inserted that as optional in my house rules document).

      I agree to an extent that there should be a class of climbs that are either automatic or you shouldn't attempt them (esp. for long distances).

      If you were forced to pick ONE ability to base climbing on, would you think Str or Dex more important? (3E used Strength, but my close friends who do climbing say Dexterity.)

  11. Not being a climber myself, I would love to hear more about this and what you think the percentages should be! (furiously taking notes)

    1. Actually, as further research, I'm scheduled to go gym-climbing for the first time next Monday, as I write this.

  12. I think the chance of success should be very high (100%) to just climb without armor IF you are strong enough and have high enough dex. I would give a base DEX / STR to each grade of climb. If you meet the minimum your chance is 100% to make it. If not then maybe a d20 modified by how much you miss the minimum. I would avoid multiple rolls or have a single roll cover at least 20-30 feet.

    The rolls should be reserved for dangerous grades, if loaded with gear, wearing restrictive clothing, or trying to move fast.

    You may want to impose a penalty on the more sedentary classes, because it really is about strength to body weight ratio, if you can't do a pull up (or several) you should not be free climbing.

    In a typical OSR D&D game this would mean clerics and magic-users would get the out of shape penalty, maybe just a minus to effective DEX or STR.

    Fighter types are in shape, but they are going to have to take off their armor to avoid massive climbing penalties.

    A thief on the other hand would not need to take off his armor and should get an effective DEX/STR bonus based on level.

    I'd frankly make the Monk just as an effective climber, except without the ability to climb in armor.

    You can play around with the STR and DEX requirements. I'd put more emphasis on DEX, especially for harder grades as that is the Thief focused stat, also there is a lot to being able to get your foot up near your shoulder, shifting your weight and the timing of movements, all DEX based.

    Another way to make climbing less all or nothing, (well one is to use ropes, but even then if you fall you still slam back into the rock, you just don't fall to your death) is to have the first fail be a slip.

    Safe climbing you always have 3 points on the rock (1 hand two feet or 2 hands 1 foot). You only go to 2 points when you need to reach, e.g. get over around something, transition to another part of a route. This is where you can die if you fail. People who free climb all the time work really hard to be able to do that 1 arm pull-up.

    So slip could be you lose one of your holds, or better yet a piece of gear.

    I'd rate a climb by grade, overall difficulty and if long enough by section where getting from a section to section would require a tricky maneuver.

    I see thieves as the point climber to set the rope when the party needs to climb, or being so good they can take penalties to quickly and quietly climb something. Lastly, Thieves should be good at route selection, seeing the way to take that has the best chance of success. Non-thieves may well pick a route that leads them to trouble.

    1. I'm totally on board with the mechanic making a large class of climbs automatic for certain climbers (e.g., for classic D&D thieves, it's pretty close to that already). And I agree with the distance -- I made the increment 30' per check in my house rules last week.

      3E has this window of "minor failure" in their checks (5 pips in 20) where you fail to progress but also don't fall. That seemed like a good idea but I found that I forgot about in practice in my last game.

  13. I feel like I need to correct you on the probability of the 3E Fighter.

    See, while Climb is a class skill for them they don't have that many skill points to spend. The Rogue gets 8+INT skill points per level; the Fighter gets 2+INT, and has Intelligence as a tertiary stat at best.

    So a typical Fighter has just two skills that they're able to "max", and need to choose between Climb, Craft, Handle Animal, Intimidate, Jump, Ride, and Swim.

    However, Climb is also a Strength skill, and Strength is quite possibly the primary score of the Fighter. You can probably safely assume the third-level Fighter to get an additional +2 bonus from that, and the fourth-level Fighter to get a +3.
    Maybe add a +1 if they've got a +2 Strength item already.
    And +2 from a Climber's Kit (80gp, weighs 5lbs.).
    And +2 if they have 5 ranks in Use Rope.
    And +2 for every person helping you climb.
    Oh yeah, and you can basically Take 10 at any point outside of combat so unless you're really bad at it you probably won't actually fail.

    3E's modifiers kind of got out of hand, to be honest, and the skill system wasn't very well thought out.

    1. Yeah, of course I was looking at all that stuff and making a decision about what to include for a presumed simulation. Probably the most obvious thing I ignored was Fighter's likely Strength (mentioned parenthetically above).

      If I include a +2 Strength bonus, then that actually matches the default Fighter statistics on 3E (2000) DMG p. 53. 3rd and 4th level fighters have no chance of falling. Actually, 1st level fighters there are exactly at the stats I stipulated above (3-in-20 chance to fall off a rope on any check, etc.).

      I think it's reasonable to not assume a Climber's Kit, inasmuch as it's not include in the PC starting package (PHB) or default NPC stats (DMG). And I'd personally rule that the Cooperation bonus is not applicable to climbing ("The DM limits cooperation as she sees fit for the given conditions."). I always ignore Take 10 because, ugh.

      Anyway, good thoughts and now we're pretty deep in the thickets of 3E. :-)