How did Venice become a city on water?

As the Roman Empire collapsed in the 5th Century, marauding Goths and Vandals drove many inhabitants of the northern Italian province of Venetia to seek sanctuary on a group of mosquito-infested islands on a swampy lagoon in the north-east. Correctly, the refugees believed the islands to be so unappealing that the invaders would simply pass them by.

The early Venetians led a precarious existence, tethering their boats beside simple wooden huts, which were raised on stilts to protect them from high tides and flooding. On some of the higher islands, houses could be built directly on patches of gravel, but elsewhere the land had to be reclaimed little by little by digging drainage canals. The threat of invasion eventually diminished, and while some of the refugees returned home, others began to make a more permanent settlement in this isolated place.

Islands linked by 400 bridges In AD 697, by which time building had begun in earnest, the settlements became an independent unit under an elected chief magistrate known as the doge.

The most central settlement, Rivo Alto (later corrupted to Rialto), was to become the heart of Venice, linking 118 separate islands with some 400 bridges. To drain the land, more than 200 canals were dug branching off the Grand Canal, the principal waterway that traverses the islands in the shape of a backwards 'S' for 2 miles (3.2 km) and which would, in centuries to come, be lined with grand palaces.

On the soft ground of the island city, buildings required the firmest of foundations. The answer was to sink a forest of larch piles. They were driven into the clay subsoil by teams of builders using wooden hammers. Then further layers of Jarch and crushed birch were packed into the foundations. Locally produced birch was the most common building material, but workmen also used clay bricks, of a rich red-brown hue, from the mainland.

To hold back rising damp in the walls, stonemasons laid a layer of white limestone - brought in blocks from nearby Istria - at the high water mark of a building. This stone was both easy to carve and highly impervious to weathering, and from the Renaissance (15th century) onwards, masons faced grander buildings entirely in this dazzlingly bright material.

Minor shifts in the foundations of buildings were a constant hazard, and structures were designed to 'flex' with the ground beneath them. Roofs, for example, were rarely vaulted, and ceiling beams were closely spaced and topped by one or two layers of wooden planks.