Rebuilding the Lighthouse of Alexandria, Block by Virtual Block

Towering over ancient Alexandria, a 460-foot lighthouse of granite and limestone known as the Pharos stood as a symbol of Hellenistic ambition and a nightly guide for mariners. Centuries of earthquakes reduced the structure to ruins, and an international archaeological team is now reconstructing it as a comprehensive digital twin, piece by virtual piece.

For nearly 1,600 years the Pharos survived dozens of tremors until an A.D. 1303 quake and another 20 years later left its stones scattered across 18 underwater acres. Visibility is poor and the seabed uneven, Dr. Isabelle Hairy said; since taking charge of the Pharos Project four years ago her team has analyzed roughly 5,000 blocks and artifacts and is reverse-engineering the lighthouse from its 14th-century collapse.

The work relies on photogrammetry to stitch thousands of two-dimensional images into precise three-dimensional models. "Try dredging those by hand. Not recommended," said Paul Cartledge, who is not connected to the operation.