 In terms of the extent of the city affected and number of destroyed buildings, the Chiado fire is often considered the worst disaster to strike the city since the 1755 Lisbon earthquake.Although it is known that the fire started with a slow combustion on the top floor of the Grandella building (which is unlikely in the event of intentional fire, that typically spreads quickly) the cause was never fully determined.In 1989 the Portuguese architect Álvaro Siza Vieira was invited by the mayor of Lisbon Krus Abecasis to oversee the reconstruction project for the area.