Castles is about the last stand of civilization against barbarism. A hundred barbarians are charging towards your castle. A handful of barricades, a wall, and a small band of heroes must hold the barbarians back.
Castles is a turn-based strategy wargame of using limited reinforcements to shore up collapsing defenses, and using the enemy's aggression to keep them away from your castle.
There are three unit types: Knights are fast strike units: they can move up to the front line quickly, and can kill many Barbarians before dying. Pikemen are cheap defensive units: they block the advance so other units can kill. Archers fire from a distance: any Barbarian in 2 spaces can be killed.