The city has sunk about 25 centimetres in the last 100 years -- or double what it sank in the previous century, the researchers calculated in data published on Tuesday in the university journal, Antiquity.

Archaeologist Albert Ammerman and geologist Charles Mcclennen, who did their research in Venice, worked out the accelerated rate of sinking, and Colgate University confirmed it on Tuesday.

The two scientists believe a loss of groundwater and a rise in sea level have caused the rate of sinking by Venice's historic palaces and homes to increase rapidly.

The loss of the underground reservoir causes the sinking of the ground on which Venice is built, the scientists say, while the sea level has risen as a result of global warming.

If true, the data means a two-billion-dollar plan to hold back the sea usinginflatable gates ``might be too little, too late,'' the newspaper USA Today said. The newspaper said that the university article comes when the famed city is just beginning its annual October-to-February struggle to contain high tides and water surges.