Holy Sepulcher
The Holy Sepulcher (alternately Sepulchre) is a tomb in Jerusalem which, in the Christian tradition, is regarded as the tomb of Jesus Christ and the site of his resurrection.
In period, Christianity was very much focussed on the veneration of relics and pilgrimage to holy places. As the tomb of Christ, the Holy Sepulcher was seen as the holiest single location in Christianity. When access to the Church of the Holy Sepulcher was seen as threatened by the Muslims, Christians in Europe launched the Crusades to reclaim them and (among other things) guarantee access.
The Holy Sepulcher was so important to the Crusaders that when the Kingdom of Jerusalem was founded in 1099 after the First Crusade, its first ruler, Godfrey of Bouillon, took not the title of King, but instead was styled Advocatus Sancti Sepulchri -- "Defender of the Holy Sepulcher."
Like many Christian pilgrimage sites in the Holy Land, the location of the Sepulcher was identified by Helena of Constantinople, mother of Constantine I, who caused a church to be built over the tomb.