The Hospital heals wounded soldiers and revives SvS dead. It CANNOT heal or revive: siege machines (repaired at Trap Factory), souls (revived at Holy Palace), deserters (recalled at Holy Palace) or dead generals (revived at Shrine). Higher level increases wounded capacity. Buildable at Keep 6; the Research Factory requires the Hospital first. For automation: the Heal function CANNOT be used while the Hospital upgrades; Revive (shown only during SvS) CAN be used while upgrading. Milestone: Lv15 Duty Officer (increases Capacity and Healing speed; ideal Blanche, then Pericles/Skanderbeg). Capacity is increased many ways beyond level: Academy research (Hospital Scale, Super/Supreme Hospital Scale, Adv Medical Power) plus Military Academy Military Drill I-III, the duty officer, wall-defense generals at red star 2 (Richard the Lionheart +30% even at star 0), a Dragon of Thebes defender (+25% Lv10, +35% Lv15), Monarch Talent Lv30 Hospital Capacity (+25%), and a temporary +50% during SvS. Keep-gated 1:1 to Lv50. Note: battlefields like Gaugamela/Constantinople have unlimited hospital capacity, so capacity boosts are meaningless there. Bot rule: do not upgrade the Hospital mid-war (healing disabled).
Original research source: Evony Guide Wiki