An extensive artificial reservoir was created in Lower Nubia, when the first Aswan dam was constructed (and heightened in three phases) between 1902 and 1933, necessitating a campaign to survey Nubian sites before they were submerged. When work began on the new Aswan High Dam in 1960, the creation of Lake Nasser, one of the largest reservoirs in the world, was initiated. A UNESCO-coordinated operation was therefore launched, not only to record the Nubian monuments threatened by this much more extensive flooding but also to dismantle and move certain monuments (including PHILAE, ABU SIMBEL and KALABSHA) to higher ground before the completion of the dam in 1971.