Suleiman the Magnificent (1494–1566), the Ottoman sultan who built the present walls around the Old City, also apparently mined the quarry, ultimately sealing it up around 1540 because of security concerns. In 1854 the American missionary James Turner Barclay followed rumors of a cavern near the Damascus Gate, and, apparently with the help of his dog, discovered the entrance.[5] Barclay and his two sons returned secretly at night and explored the cave.[5]