Final answer:
Christian control of Jerusalem was temporally restored by Frederick II through the Treaty of Jaffa during the Sixth Crusade, not by military conquest during the Third Crusade. Despite Richard the Lionheart's efforts, he did not recapture Jerusalem from Saladin.
Step-by-step explanation:
Jerusalem was temporarily restored to Christian control by efforts of various Crusader leaders; however, it was Frederick II, Holy Roman Emperor, who managed to gain control of Jerusalem through diplomacy rather than outright warfare. During the Sixth Crusade, Frederick II negotiated the Treaty of Jaffa with Sultan al-Kamil in 1229, which resulted in the restoration of Jerusalem, Nazareth, and Bethlehem to Christian control without major conflict. This tenure of control was short-lived, and Jerusalem returned to Muslim control after the expiry of the ten-year truce agreed upon in the Treaty. It is important to note that during the Third Crusade, Richard the Lionheart did engage in battles in the region and secured some territories, including the city of Acre, but he did not recapture Jerusalem, failing to reach an agreement with Saladin to cede the city to Crusader control.