The English Civil War battle of Roundway Down was fought on July 13, 1643, at the eponymous hill north of Devizes in Wiltshire. Lord Henry Wilmot, Earl of Rochester , commanding the Royalist forces, won a crushing victory over the Parliamentarian Sir William Waller.

Lord Ralph Hopton's army had formerly drawn with Waller at Lansdowne, but was weakened and moved to Devizes, which Waller besieged with his artillery. However, the coming of cavalry reinforcements from Oxford, led by Prince Maurice (nephew of King Charles I), forced Waller to draw off from the siege and ready for battle.

Maurice and Wilmot charged, with partial success, Waller's cavalry fleeing before them, but the infantry held its ground. Hopton, however, saw the opening and sallied forth from Devizes to attack from behind. The Parliamentary line melted away, losing more than a thousand men killed or captured.

This was effectively the end of Parliamentary support in the West country; Prince Rupert entered Bristol on July 25.