The First Crusade (1095-1099) was the first of a number of crusades that attempted to recapture the Holy Land, called for by Pope Urban II at the Council of Clermont in 1095.
Urban called for a military expedition to aid the Byzantine Empire, which had recently lost most of Anatolia to the Seljuq Turks.
The resulting military expedition of primarily Frankish nobles, known as the Princes' Crusade, not only re-captured Anatolia but went on to conquer the Holy Land (the Levant), which had fallen to Islamic expansion as early as the 7th century, and culminated in July 1099 in the re-conquest of Jerusalem and the establishment of the Kingdom of Jerusalem.
The expedition was a reaction to the appeal for military aid by Byzantine Emperor Alexios I Komnenos.
Urban's convocation of the Council of Clermont was specifically dedicated to this purpose, proposing siege warfare against the recently occupied cities of Nicaea and Antioch, even though Urban's speech at Clermont in the testimony of witnesses writing after 1100 was phrased to allude to the re-conquest of Jerusalem and the Holy Land as additional goals.