After Attila the Hun destroyed Altinum in 452, the Veneti of the mainland sought safety in the only place no army would follow -- the shallow, marshy islands of the lagoon. Torcello, at the lagoon's northern end, became their refuge. The settlement grew slowly under the nominal protection of the Byzantine Exarchate of Ravenna, though in practice the island was too remote for Constantinople to govern effectively. Lombard and Frankish invasions over the following two centuries drove successive waves of urban refugees to Torcello, including the Bishop of Altino himself, who transferred his seat to the island in 638. He brought with him the relics of Saint Heliodorus, Altino's patron, a symbolic act that declared the old city dead and the new one legitimate. Torcello maintained close trading ties with Constantinople, profiting from the salt marshes that surrounded it and from a harbor that served the east-west trade routes Byzantium controlled.

By the 10th century, Torcello had become a substantial settlement -- recent archaeological estimates suggest a peak population near 3,000, though older sources placed the figure far higher at 10,000 to 35,000. Whatever the true number, Torcello was for a time a more powerful trading center than the collection of islands to its south that would become Venice. Salt was the economic backbone, and the harbor made the island a lucrative re-export market. But the lagoon was shifting. By the 14th century, the marshes around Torcello had expanded, partly from subsidence of the land itself. Navigation through the laguna morta -- the dead lagoon -- grew impossible. Traders stopped calling. Plague compounded the decline, and malaria spread through the stagnant waters. Families left for Murano, Burano, or the Rialto district that was consolidating into the Venice we know. The palazzi were stripped for building materials, their marble and stone repurposed in the very city that was replacing Torcello.

Almost everything Torcello built has vanished -- except the cathedral. The Cathedral of Santa Maria Assunta, founded in 639, is one of the oldest religious buildings in the Veneto. Its interior holds 11th and 12th century Byzantine mosaics, including a vivid Last Judgement that covers the western wall and a solemn Virgin Hodegetria floating against a vast gold background in the main apse. Beside the cathedral stands the church of Santa Fosca, built in the shape of a Greek cross and ringed by a semi-octagonal portico. The Museo Provinciale di Torcello occupies two 14th century palaces that once housed the island's council and archives. And there is the stone chair known as Attila's Throne, which has nothing to do with the Hun king but may have been used by the island's chief magistrate or bishop. It sits outdoors, worn smooth by centuries, a seat of power in a place that has none.

Torcello's emptiness has drawn writers who needed solitude or found in the island a particular kind of melancholy. Ernest Hemingway stayed here in 1948, working on Across the River and Into the Trees at the Locanda Cipriani, the inn that remains one of the few functioning establishments on the island. Representations of Torcello and its lagoon appear throughout the novel. Daphne du Maurier set her short story Don't Look Now on the island, its deserted canals and crumbling architecture providing the unsettling atmosphere the story required. There is also the Ponte del Diavolo, the Devil's Bridge -- a small stone span without railings that crosses one of Torcello's canals, its name part of a local legend. The bridge is modest, easy to miss, but it captures something essential about the island: even the small things here carry old, strange names.

Arriving on Torcello requires a vaporetto ride through the northern lagoon, past Burano's painted houses, into increasingly quiet water. The landing delivers you to a path along a canal lined with overgrown vegetation. There are no crowds. The silence is not the hush of a museum but the genuine quiet of a place where almost no one lives. The cathedral's mosaics gleam in the dim interior, their gold catching whatever light enters through the high windows, as beautiful now as when they were set into wet plaster a thousand years ago. Outside, the marshes stretch in every direction, and the lagoon dissolves into sky at the horizon. Venice is somewhere to the south, invisible, the city that Torcello made possible and that then forgot it. Standing among the ruins, the mathematics of the place are stark: a civilization that once filled these islands reduced to ten residents and a handful of tourists who take the boat back before dark.