The manual:
"On average, city levels generate a small militia 50% of the time per level
On average, ports levels generate a small militia 25% of the time per level
On average, city fortications levels and Depots levels generate a garrison
militia 100% of the time per level"
in a PBEM game I just lost Genoa (lvl 4 city, lvl 1 fort, harbor) with 100% loyalty to one Pompeian cavalry unit, in addition to Faesulae (lvl 4 city, lvl 1 fort), because no garrisons were generated. Shouldn't the fort ensure the spawning?