Ken Munsie: 126. The city of islands

Venice is built on 118 islands in the marshy Venetian Lagoon, and its history as an autonomous region of the Eastern Roman Empire dates back to 560 AD.

Over the centuries the city has grown both in size and importance, however today the seat of government and business for the Veneto region has shifted to the neighbouring mainland city of Mestre, and Venice has become primarily a tourist attraction catering for millions of visitors each year.

And one of the most beautiful aspects of the city is its ancient architecture - much of which lines the canals that weave their way throughout the city.

The buildings of Venice are constructed on closely spaced wooden piles – mostly made from the trunks of alder trees - a wood noted for its water resistance - and most of these piles are still intact after centuries of submersion.

The foundations rest on the piles, and buildings of brick or stone sit above these footings. The piles penetrate a softer layer of sand and mud until they reach a much harder layer of compressed clay. Submerged by water, in oxygen-poor conditions, wood does not decay as rapidly as on the surface.

During the 20th century, when many artesian wells were sunk into the periphery of the lagoon to draw water for local industry, Venice began to subside notably. It was realised that extraction of water from the aquifer was the cause. The sinking has slowed markedly since artesian wells were banned in the 1960s. However, the city is still threatened by more frequent low-level floods that creep to a height of several centimetres over its quays, regularly following certain tides. In many old houses, the former staircases used to unload goods are now flooded, rendering the former ground floor uninhabitable.