The Crusader states in 1165
The Kingdom of Jerusalem was founded in 1099 at the end of the First Crusade. It was the third of four Christian territories to be established by the crusaders, following the County of Edessa and the Principality of Antioch, and followed by the County of Tripoli. Jerusalem's first three rulers, Godfrey of Bouillon (1099–1100), his brother Baldwin I (1100–1118), and their cousin Baldwin II (1118–1131), expanded and secured the kingdom's borders, which encompassed roughly the same territory as modern-day Israel, Palestine, and Lebanon. During the kingdom's early decades, the population was swelled by pilgrims visiting the holiest sites of Christendom. Merchants from the Mediterranean city-states of Italy and France were eager to exploit the rich trade markets of the east.
William's family probably originated in either France or Italy, since he was very familiar with both countries. His parents were likely merchants who had settled in the kingdom and were "apparently well-to-do", although it is unknown whether they participated in the First Crusade or arrived later. William was born in Jerusalem around 1130. He had at least one brother, Ralph, who was one of the city's burgesses, a non-noble leader of the merchant community. Nothing more is known about his family, except that his mother died before 1165.
As a child William was educated in Jerusalem, at the cathedral school in the Church of the Holy Sepulchre. The scholaster, or school-master, John the Pisan, taught William to read and write, and first introduced him to Latin. From the Historia it is clear that he also knew French and possibly Italian, but there is not enough evidence to determine whether he learned Greek, Persian, and Arabic, as is sometimes claimed.
Around 1145 William went to Europe to continue his education in the schools of France and Italy, especially in those of Paris and Bologna, "the two most important intellectual centers of twelfth-century Christendom." These schools were not yet the official universities that they would become in the 13th century, but by the end of the 11th century both had numerous schools for the arts and sciences. They were separate from the cathedral schools, and were established by independent professors who were masters of their field of study. Students from all over Europe gathered there to hear lectures from these masters. William studied liberal arts and theology in Paris and Orléans for about ten years, with professors who had been students of Thierry of Chartres and Gilbert de la Porrée. He also spent time studying under Robert of Melun and Adam de Parvo Ponte, among others. In Orléans, one of the pre-eminent centres of classical studies, he read ancient Roman literature (known simply as "the Authors") with Hilary of Orléans, and learned mathematics ("especially Euclid") with William of Soissons. For six years, he studied theology with Peter Lombard and Maurice de Sully. Afterwards, he studied civil law and canon law in Bologna, with the "Four Doctors", Hugo de Porta Ravennate, Bulgarus, Martinus Gosia, and Jacobus de Boragine. William's list of professors "gives us almost a who's who of the grammarians, philosophers, theologians, and law teachers of the so-called Twelfth-Century Renaissance", and shows that he was as well-educated as any European cleric. His contemporary John of Salisbury had many of the same teachers.