Saint Hilarion was originally a monastery, named after a monk who allegedly chose the site for his hermitage, with a monastery and a church built there in the 10th century. Starting in the 11th century, the Byzantines began fortification. Saint Hilarion formed the defense of the island with the castles of Buffavento and Kantara against Arab pirates raiding the coast. Some sections were further upgraded under the Lusignan rule, who may have used it as a summer residence. During the rule of Lusignans, the castle was the focus of a four-year struggle between Holy Roman Emperor Frederick II and Regent John d' Ibelin for control of Cyprus.
The castle has three divisions or wards. The lower and middle wards served economic purposes, while the upper ward housed the royal family. The lower ward had the stables and the living quarters for the men-at-arms. The Prince John tower sits on a cliff high above the lower castle. The church lies on the middle ward. The upper ward was reserved for the Royals and can be entered via a well-preserved archway. Farm buildings are located in the west close to the royal apartments. Along the western wall, there is a breathtaking view of the northern coast of Cyprus, overlooking the city of Girne, from the Queen's Window.
Much of the castle was dismantled by the Venetians in the 15th century to reduce the up-keeping cost of garrisons.