Armies | Medieval Kingdoms Wiki

Regiments are raised in your provinces from the campaign menu (C) and grouped into armies. Each regiment is one company slot in a battle.

Infantry, 15 men: 20 Grain, 10 Lumber. Upkeep 4 Grain, 2 Leather.
Men at Arms, 8 men: 20 Grain, 20 Iron, 10 Gold. Upkeep 4 Grain, 4 Leather, 2 Iron, 1 Gold.
Cavalry, 6 men: 25 Grain, 20 Horses, 5 Gold. Upkeep 6 Grain, 4 Leather, 2 Horses. Needs a province that makes Horses.
Skirmishers, 7 men: 15 Grain, 10 Lumber, 5 Cloth. Upkeep 3 Grain, 1 Leather.
Command, 3 men: free, one per nation. It brings no tickets and takes no battle slot.

Every regiment except Command can be raised small, standard or large: Infantry 10/15/20 men, Men at Arms 5/8/10, Skirmishers 5/7/9, Cavalry 4/6/8.
Cost, upkeep and tickets all scale with the size, so no size is a better deal per man. Pick the size your companies can actually fill.

Professional regiments pay the full cost and fight with full kit.
Militia cost half, pay only Grain for upkeep, and can only be raised in your home provinces. They fight with basic kit and bring 60% of the tickets.

A standard professional regiment brings 1,125 tickets to a battle (see Diplomacy Battles).
A new regiment rallies for 6 hours: it starts with only a few tickets and fills up to full over that time.

Battles cost regiments strength. A regiment heals 20% a day, but only standing in a province your nation owns and controls, and not while a battle is owed there.
Rehire to fill a regiment at once with Gold: a full standard regiment costs 12 Gold for Infantry or Skirmishers, 25 for Men at Arms or Cavalry. Missing a third costs a third; militia pay half.
A regiment that falls below 20% strength is disbanded.

6 hours a land province, 4 if the army is all cavalry, 2 for a Command on its own.
12 hours to cross a strait, 8 hours a sea province by ship.
Armies may enter your own land, unplayed land, an ally's land, land of a nation that gave you Military Access, and land of a nation you are at war with.