The tower of Pisa leaned more in 1988 than the previous year but is expected to stand for more than another century, an expert who measured the incline said Sunday.

Giuseppe Toniolo, head of a group charged with the preservation of the monument, said that during the past year the medieval tower shifted 0.0508 inches.The 180-foot tower leaned 0.028 inches in 1987.

Toniolo said the tower has leaned an average of 0.0508 inches over the past 60 years.

"Some years it's a little less, some years a little more," he said.

Toniolo said if the tower continues to lean at the current rate it would topple over in 100 to 150 years.

Begun in 1173, the tower was only 34 feet high when the soil underneath it began to give way, causing it to tilt. It was completed between 1360 and 1370.