Venetian word, from "muro" (wall). The massive structure built up as a protection from the sea erosion of the Venice lagoon. Sea defence work built up of Istrian stone and pozzolana along the littorals of Malamocco, Pellestrina and Sottomarina by the mathematician Bernardo Zendrini starting from 1739 on commission of the Venice Republic. They are frontal barriers built up in order to prevent the sea from attacking and eroding the banks. They were planned in 1716 by Father Vincenzo Maria Coronelli, a priest form Ravenna who worked mainly in Venice at the convent of Santa Maria Gloriosa dei Frari, and who was a very important cosmographer and geographer during the age of the Serenisssima. The murazzi were seriously damaged during the strong sea storm on the 4th October 1966.
Source: Garzanti on line