Since the days of ancient Egypt, obelisks have been employed by architects to signal the presence of sacred sites to pilgrims. "It is the calling card of the city of stone," says Claudio D'Amato Guerrieri, professor of architectural design at Bari Polytechnic.

This week, a 15.5-metre example will loom over the red-brick warehouses and docks of Venice's medieval shipyard, marking the entrance to a special exhibition that is part of the city's 10th Architecture Biennale. Appropriately, the show is called Cities of Stone and the material is its undisputed star.