For instance, 12,000 tree trunks, each about 14 centimeters (6 inches) thick and up to 3 meters (10 feet) long, were used in the construction of the Rialto Bridge alone in the 13th century. The Campanille of St. Mark supposedly rests on 100,000 posts, and the Santa Maria della Salute church on more than a million. No one can say exactly how many oak, elm, alder and poplar trees were sunk in the bottom of the lagoon. It must certainly be an unimaginably large number. Not only Venice's Italian hinterland, but also the coasts of Istria and Dalmatia on the opposite side of the Adriatic were almost completely cleared at the behest of Venetian builders. The barren landscapes of the eastern Adriatic coastline still bear witness to this deforestation.
The young city on the water grew -- but life wasn't easy. From September to April, it was threatened by hot Mediterranean sirocco winds. Storms "overflowed the Lidi and the islands of Venice with such force that it felt like another biblical Great Flood," wrote scholar and lagoon researcher Jacopo Filiasi. Masses of salty water ran into the houses, spoilt food supplies, damaged goods and threatened to salinate the wells, especially if the guards weren't able to seal them in time with clay. The enormous water pressure from the Adriatic also prevented the swollen rivers flowing down from the Alps from draining, thus driving water levels in the lagoon even higher.
In an attempt to hold back the tides, for centuries, the Venetians erected sea walls made of tamarisk shrubs, breakwaters and moles. At particularly critical or important points, they built palisades known as palades made of tree trunks. Double or triple rows of wooden piles linked by planks or iron bars formed large rectangular boxes. Filled with rocks, rubble and sand and placed by the lagoon, they acted as breakwaters.
But it wasn't a permanent solution, not least because of the wood thieves. As an 18th-century chronicler complained: "Apart from the devastating effect of the sea, the palades are also jeopardized by human wickedness, for on dark, stormy nights, people destroy all this work merely for a little wood and a handful of nails."
From the 14th century on, anyone who endangered the city's flood defenses in any way risked getting a hefty fine or even a public flogging. Felling pine trees, burning off grass, driving cattle across the dykes and removing reeds or sand were all forbidden. An old inscription from the Magistrato Alle Acque, the water protection agency, warned: "Whosoever shall dare to damage this common asset should not be punished less severely than those who damage the walls of the town. This edict shall remain in force in perpetuity."
Tuscan Clay Saves City
But even without human wickedness, the palades were not a permanent solution, either. They didn't hold back the floodwaters for long, and constantly needed to be repaired. "The palisades were ruinously expensive," writes Italian historian Piero Bevilacqua. "They cost the city-state thousands of ducats a year and seemed to be merely a Sisyphean task."
Tuscany had a solution to the problem. Both there and farther south in Rome, harbor walls had long been built using a kind of waterproof cement. Venetian lagoon expert Bernardino Zendrini finally came across this puzzolano clay in the 18th century during a trip to Tuscany.
At first, the Venetians didn't trust this new material. In 1738, they built a small first test wall near Malamocco. The following year, they built a 16-pace-wide harbor mole. "This cement bonds extremely well," noted the then-head of the water agency in amazement. "And it is so resistant that no force can separate it. Far more remarkable still, mixed with water, it quickly becomes almost as hard as stone."
In 1740, the senate released the first funds for the construction of the Murazzi, gigantic barriers made of Istrian marble and rock cemented together with puzzolano clay. For the next 30 years, the Venetians worked on an enormous wall stretching more than 10 kilometers (6 miles) from Malamocco via San Pietro in Volta and Pellestrina to Chioggia.
At the time, this wall cost the astronomical sum of 20 million Venetian lire, but the investment was worth it. Although the Murazzi also needed repairing now and again, they outlasted the Venetian republic and protect the city to this day against attack from the waters.
Silt Posed New Threat
The storm floods of the Adriatic outside the lagoon's porti weren't the only threat. Far more dangerous for the city's citizens were the rivers that gushed into the basin carrying stones, earth and sand with them.
The Venetians didn't notice the danger until relatively late. At first, the damage was almost imperceptible. But even if it had been noticed in time, it wasn't clear which elements were conspiring against the city. To this day, experts argue vehemently over the role local factors play and what influence the global ebb and flow of the oceans have.
At any rate, the Venetians realized in the 15th century that their city-state was in terrible danger because of the water they both depended on and had to protect themselves against. For about 300 years, water levels in the lagoon had been falling. Soon they would find themselves stranded, and it seemed only a matter of time before their world came to an end.
Nearby Ravenna provided disturbing evidence of what could happen. Just like Venice, Ravenna was founded in the lagoon. In the 5th century, it even became an imperial city. But, bit by bit, the magnificent city silted up, gradually losing importance and eventually disappearing into obscurity. Today, Ravenna is located 9 kilometers (6 miles) from the coast.
It was therefore hardly surprising that, in the 16th century, the famous doctor and hydrologist Girolamo Fracastoro warned that the lagoon would "dry out from the sea and become marshy, either because it silts up or because the sea withdraws from the entire bay." The scientist couldn't imagine "any human power that can resist that."
Most contemporaries took a similarly dramatic view of the situation. Fears grew that the decreasing amounts of seawater would increase the prevalence of plague and malaria in the lagoon. One contemporary predicted that the constant inflow of fresh water would "render the air so foul in summer that Venice will become uninhabitable." According to an official document, the experts saw only one possible solution: "increasing the amount of water." So they tapped the canals on the mainland.
'The Source of All Evil'
The results were fatal: Water diverted into the lagoon in this way spread out across the flat basins, evaporated in summer and -- as noted in a sarcastic report by officials following the expensive yet ultimately doomed large-scale rescue operation -- managed only to "produce the worst possible air quality." Then someone had the revolutionary idea of turning off the supply of fresh water altogether, that is, to divert the rivers flowing into the lagoon in such a way that they emptied not into the bay, but directly into the sea.
Back in 1324, attempts had already been made -- and just as quickly abandoned - to divert the River Brenta, which the Venetians considered "the source of all evil." At exactly the same time, the San Nicolo di Lido entrance to the lagoon silted up. The Venetians were convinced it was a side-effect of their large-scale surgical intervention into the maritime world.
Even though it was probably unnecessary, the Venetians forced the Brenta back into its old course in 1360. Eight years later, the little river was back in the canal. The same pattern was repeated over and over. Each time such massive projects were undertaken, the outcome was unpredictable. Building projects "turned out to be the greatest threat for the lagoon," wrote mathematician Bernardino Zendrini in the 18th century, "even though they were first praised as the most effective remedy."
In the early 16th century, with the silting-up progressing apace, the powers-that-be believed there was only one solution: Not just the Brenta, but also the other "plague-bringing venomous snakes," as even official documents termed them, were to be diverted. That meant the Musone, Tergola, Marzenego and Dese rivers -- as well as the Piave. But after the authorities had tried in vain for a century to control the Piave's path with dams, its flood waves charted their own course in 1683. Now the Sile could fit into the Piave's abandoned riverbed, and after the most northerly tributary of the Po, the Po delle Fornaci, was also diverted, the deadly danger of silting up was finally averted.