Technology is another answer. Most of the forms of armor didn't all exist in the same places at the same times... Maille (D&D "Chainmail", which is a Victorian-era misnomer for what was called a Coat of Maille, back in the day) was used from the Bronze Age up through 19th century Asia. In Roman times, it was called Lorica Hamata. The Centurion's armor was Lorica Segmentata, and about the only other forms were leather and cloth outfits. During Rome's time, the change from Bronze to Iron occurred, so the materials that the armor was made from did, as well (Hadrian's Column shows that his troops had iron armor, for instance).
If you set up your campaign in a similar way, Breastplates and "Chainmail" may be the best armor available. Again, as already pointed out, these armors are hotter, heavier, and pretty hard to swim in. Set your campaign in a Tropical realm, and require heat checks (DC:20 Fortitude saves) every half-hour in Heavy Armor, and every hour in Medium. Two hours in Light. Failure gives Heat Exhaustion, with further rolls for Heat Stroke, thereafter, unless the armor is removed, the warrior cooled down, and rested until the exhaustion wears off.
This, combined with slower movement, should be enough. Later on, when the PCs start adventuring farther afield, you can introduce them to plate in Italia, or whatever. Since most long-distance travel in the ancient world was accomplished by ship, the "Paladin's PJs" (or Maille Hauberks - Chain Shirts, in D&D parlance) should remain quite common.
The Nehwon campaign sourcebook took the "armor is for trouble-makers" approach, and made leather the skullduggers' choice, as it was easy to conceal. If ypu choose to make armor illegal in your base country, then you really will be limiting PC choice (and watch out for that armor addition in the DMG that makes it appear as normal clothing)! You'll basically be limiting the PCs to Cloth, Disguised Leather & Studded Leather, Mithral Shirts (if worn under clothing), and perhaps Dastana and Brigandine (Medium armor which looks the same as studded leather, but the studs hold small metal plates between two layers of leather... found in WotC's Arms & Equipment Guide, IIRC).
IMHO, making armor illegal is a "sucky" way of doing it. Using a (Sub-)Tropical clime with water-based canal travel works much better. If you go with this, hand out a lot of +2 Circumstance Modifiers for doing "smart things", like stepping into a pool or stream to cool off, taking extra salt & water to prevent Heat Exhaustion, etc. That drops the DC from 20 to 18, and allows for a few more hours' adventuring.
If you go with the "Heat" explanation, be sure to show armored guards occassionally passing out, while on duty, guards coming off-shift and stripping off their hot & sweaty armor, Guards & Mercenaries taking off their helmets to dunk their sweat-dripping heads in the horse troughs, and other such stuff. Play up the high heat and humidity in your descriptions, and describe to the PCs how hot and uncomfortable being in their armor is. THEN make them roll the Fortitude Saves!
I did the "Sub-Tropical Clime" in one game I ran, and had one PC (Flint Farcaster) refuse to lose the Fullplate Armour... He always made his rolls vs. Heat Exhaustion, too... somehow!
If you set up your campaign in a similar way, Breastplates and "Chainmail" may be the best armor available. Again, as already pointed out, these armors are hotter, heavier, and pretty hard to swim in. Set your campaign in a Tropical realm, and require heat checks (DC:20 Fortitude saves) every half-hour in Heavy Armor, and every hour in Medium. Two hours in Light. Failure gives Heat Exhaustion, with further rolls for Heat Stroke, thereafter, unless the armor is removed, the warrior cooled down, and rested until the exhaustion wears off.
This, combined with slower movement, should be enough. Later on, when the PCs start adventuring farther afield, you can introduce them to plate in Italia, or whatever. Since most long-distance travel in the ancient world was accomplished by ship, the "Paladin's PJs" (or Maille Hauberks - Chain Shirts, in D&D parlance) should remain quite common.
The Nehwon campaign sourcebook took the "armor is for trouble-makers" approach, and made leather the skullduggers' choice, as it was easy to conceal. If ypu choose to make armor illegal in your base country, then you really will be limiting PC choice (and watch out for that armor addition in the DMG that makes it appear as normal clothing)! You'll basically be limiting the PCs to Cloth, Disguised Leather & Studded Leather, Mithral Shirts (if worn under clothing), and perhaps Dastana and Brigandine (Medium armor which looks the same as studded leather, but the studs hold small metal plates between two layers of leather... found in WotC's Arms & Equipment Guide, IIRC).
IMHO, making armor illegal is a "sucky" way of doing it. Using a (Sub-)Tropical clime with water-based canal travel works much better. If you go with this, hand out a lot of +2 Circumstance Modifiers for doing "smart things", like stepping into a pool or stream to cool off, taking extra salt & water to prevent Heat Exhaustion, etc. That drops the DC from 20 to 18, and allows for a few more hours' adventuring.
If you go with the "Heat" explanation, be sure to show armored guards occassionally passing out, while on duty, guards coming off-shift and stripping off their hot & sweaty armor, Guards & Mercenaries taking off their helmets to dunk their sweat-dripping heads in the horse troughs, and other such stuff. Play up the high heat and humidity in your descriptions, and describe to the PCs how hot and uncomfortable being in their armor is. THEN make them roll the Fortitude Saves!
I did the "Sub-Tropical Clime" in one game I ran, and had one PC (Flint Farcaster) refuse to lose the Fullplate Armour... He always made his rolls vs. Heat Exhaustion, too... somehow!
