Acre remained in Muslim hands until it was unexpectedly besieged by King Guy of Lusignan—reinforced by Pisan naval and ground forces—in August 1189. The siege was unique in the history of the Crusades since the Frankish besiegers were themselves besieged, by Saladin's troops. It was not captured until July 1191 when the forces of the Third Crusade, led by King Richard I of England and King Philip II of France, came to King Guy's aid. Acre then served as the "de facto" capital of the remnant Kingdom of Jerusalem in 1192. During the siege, German merchants from Lübeck and Bremen had founded a field hospital, which became the nucleus of the chivalric Teutonic Order. Upon the Sixth Crusade, the city was placed under the administration of the Knights Hospitaller military order. Acre continued to prosper as major commercial hub of the eastern Mediterranean, but also underwent turbulent times due to the bitter infighting among the Crusader factions that occasionally resulted in civil wars.