The piety of the Middle Ages, ever wont to express its spiritual emotions in concrete shape, had long found in pilgrimages to holy places a favourite method of kindling its religious zeal and atoning for past misdeeds. Of all pilgrimages, the most meritorious was that to the sacred spots where Christ had lived His earthly life and where the Christian faith first arose. From the days of St. Jerome, Jerusalem was the chief centre of holy travel; and from the days of Helena, the mother of Constantine, faithful Christians had sought to identify and consecrate the exact places of the Lord’s birth, suffering, and resurrection. A great Christian Basilica, built by Helena’s pious care, marked the site of the Holy Sepulchre, and men believed that divine agency had led to the discovery of the True Cross on which Jesus had suffered. As long as the Roman Empire remained in its integrity, pilgrimages to the Holy Land were safe and easy. Even the conquest of Syria by the Caliph Omar did not make them impossible. A noble mosque—the mosque of Omar—was built on the site of the Jewish Temple, but the custody of the Holy Sepulchre and the other sacred spots remained in Christian hands, and the places themselves were treated with respect and reverence by the tolerant Arabs, to whom Jerusalem was a city as venerable as to the Jew or Christian. All through the early Middle Ages the swarm of pilgrims continued. The risks of the journey through the lands of Islam increased the merit of the act. But with the break-up of the great Caliphate, the holy places became for the first time dangerous to the Christian wayfarer. In the second third of the tenth century Jerusalem was ruled by the fanatical Ikshidites (934–969), but in 969 the Fatimite Caliphs of Cairoan conquered Egypt and Syria, and for a time pilgrimages again became easy. The Fatimites were Shiites, and their dissensions from the orthodox Sunnites made them perforce tolerant of other creeds. Only the mad Caliph El Hakim (996–1021), who contemplated the destruction of the Holy Sepulchre, stayed for a time the influx of the faithful. The religious revival that flowed from Cluny, and the greater peacefulness of western Europe, led to a vast throng of pilgrims during the seventy years that succeeded El Hakim’s death. The fierce Fulk the Black of Anjou thrice visited the holy places. Robert, Duke of Normandy, abandoned his son William to go on pilgrimage in 1035. In 1064 Archbishop Siegfried of Mainz headed a band of 7000 penitents to Jerusalem. The conversion of the Hungarians under St. Stephen again opened up the land route through the Danube valley and the Greek Empire, which men preferred to the stormy sea swarming with Saracen pirates. [Sidenote: The Turkish Conquest of Palestine.]