2e BattleSystem rules, loosely based on 2e AD&D RPG rules, are pretty good. The PDF can be downloaded for $4.99 USD. These rules do utilize polyhedral dice: d4, d6, d8, d10, and d12. One die type per attacking figure within a Unit of troops, so you'll need plenty of poly's to play it if you have large Units; I've rolled 50 d6 in games in the past, for just one attack -- I like bucket-o-dice games.
Ignore the magic rules/spells. Use/ignore the hero rules, as well.
They cover Screws, Picks, Lt. & Hvy. Catapults, Ladders, Ballistae, Trebuchets, Rams, Siege Towers, and even mining and counter-mining.
Crude black powder arms are included, but they can easily be ignored. The fantasy elements are also easily ignored.
If you want a simpler, d6-only based, non-bucket-o-dice game, I would suggest Chainmail: PDF for $4.99 USD; softcover book for $7.99 USD; or PDF + softcover book for $8.49 USD. Ignore the fantasy supplement, as desired. This is the game which led to D&D being published in 1974, so of possible gaming history interest. Cheers!
gets medieval.
