The Prison holds captives (soldiers and generals) taken in PvP. Captured SOLDIERS -> Labor (yields resources equal to 4 hours of your city's BASE production only, excluding research/green bonuses; consumes 1,000 captives, 6h cooldown endable with Gems) or Release (yields 50 Prestige fixed regardless of Prison level; consumes 1,000 captives, 6h cooldown, not shortenable). Captured GENERALS: leave imprisoned (released for Gold if the enemy pays Gems, or auto-freed after a time limit), Release unconditionally, or Execute (dead general then revived at the Shrine). Higher Prison level increases Prison Capacity and Captive Rate. Buildable at Keep 11 (also needs Quarry; early levels Quarry-gated, raise Quarry first). Imprison menu unlocks at Keep 15, and generals can only be captured if both sides are Keep 15+. All menus usable during upgrade. Captives come only from PvP wins between server players or SvS enemy-server fights (not NPC sub-cities, barbarians or battlefields). If your main city is broken into, all imprisoned generals are released. Keep-gated, Power ~62M at Lv50. For an economy bot, the Prison is a minor PvP-derived resource/prestige source, not a core economy lever.
Original research source: Evony Guide Wiki