William Longespée, 3rd Earl of Salisbury (In or before 1167 – 7 March 1226) ("Long Sword", Latinised to de Longa Spatha) was an Anglo-Norman nobleman, primarily remembered for his command of the English forces at the Battle of Damme and for remaining loyal to his half-brother, King John.

[8] During the reign of King John, Salisbury was at court on several important ceremonial occasions and held various offices: High Sheriff of Wiltshire; lieutenant of Gascony; constable of Dover; and Lord Warden of the Cinque Ports; and later warden of the Welsh Marches.

In the civil war that took place the year after the signing of the Magna Carta, Salisbury was one of the leaders of the king's army in the south.

He held an influential place in the government during the king's minority and fought in Gascony to help secure the remaining part of the English continental possessions.

Salisbury's ship was nearly lost in a storm while returning to England in 1225, and he spent some months in refuge at a monastery on the French island of Ré.

[14] One reliable source, however, states that "there is little evidence [of murder] aside from Roger of Wendover's account in Flores Historiarum".

The 1762 novel Longsword by Irish writer Thomas Leland was based on his life, which itself inspired the 1767 play The Countess of Salisbury by Hartson Hall that premiered at the Haymarket Theatre in London.