The crusades

In 1095, Pope Urban II (1088-1099) organized the first crusade, to fight the Turks who conquered Jerusalem following the request for support by Alexius I Comnenus, and also trying to reunite Western and Eastern Church under papal authority: Godfrey of Bouillon conquered Jerusalem and the Palestine in 1099.

Siege of Jerusalem

In 1144 the Turks conquered Edessa and a second crusade was announced by Pope Eugenius III in 1147-1149, leaded by Conrad III and Louis VII to defend Jerusalem: the crusade wasn't successful and Jerusalem was conquered by Saladin in 1187.

A third crusade was organized by Pope Gregory VIII in 1189-92, leaded by Philip II of France, Richard I of England and Frederick I, Holy Roman Emperor, but also this crusade was not a successful one.

The religious meaning of the first crusades was progressively abandoned in the following ones, mainly used as military action against the Byzantine and Ottoman Empires. The forth crusade was organized by Pope Innocent III in 1202-04, with the intention of invading the Holy Land through Egypt, but the Venetians gained control of this crusade and diverted it to conquer Zadar and Constantinople, defending the control of the commercial exchange with the eastern countries. A Latin Empire was established in Greece and Thrace, but it was defeated by the Byzantine Emperor Michael VIII Palaeologus in 1261.

Additional crusades were organized till 1254 (in 1213 by Pope Innocent III, in 1228 by Frederick II, by Louis IX of France  in 1248 and 1270, and by Edward I of England in 1271), without being able to take the control of Jerusalem, but with important consequences from a military and commercial point of view.