Which French king was captured during the Seventh Crusade?

Louis IX was the French king captured during the Seventh Crusade. He led the expedition to Egypt in 1248, hoping to strike at the Ayyubid power that protected Muslim control of Jerusalem.

The crusaders captured Damietta in 1249, but their advance toward Cairo stalled at Mansurah. Disease, flooding, supply problems, and fierce Egyptian resistance weakened the army. During the retreat in April 1250, Louis surrendered after the crusaders were defeated at the Battle of Fariskur.

Louis was held at Mansurah while negotiations took place. His release required the surrender of Damietta and a large ransom, traditionally given as 400,000 livres. He then spent several years in the Levant strengthening remaining crusader strongholds before returning to France.

A common mix-up is with Richard I, who was captured after the Third Crusade in 1192 while traveling through Europe. Louis IX was captured during the Seventh Crusade and later died during his own Eighth Crusade in 1270.