Rams and ballistae destroy hard targets on a d10 roll whose requirement drops by one each successive turn.
How it works
A ballista shooting ball shot at a wall, vessel or engine that inflicts at least one casualty then rolls d10: 10 destroys the target, then 9-10 next turn, 8-10 the turn after and so on, provided the shooter does not change target. Battering rams roll the same way against gates, walls and towers in the melee phase, and stones dropped from walls destroy rams, towers and mantlets by the same method. Stone walls give -2 and fenders -1 to attackers.
A battering ram destroys a gate, wall or tower by rolling a single 0 -10. The first time a 10 is required, the next turn a 9 or 10 is required, third tum a 8, 9 or 10 is required and so on.