By Rob Picheta and Livia Borghese, CNN

TUSCANY — The Leaning Tower of Pisa has slowly started defying its name, losing four centimeters of its tilt over the past 17 years.

The movement, roughly 1.5 inches, comes after extensive consolidation work done between 1993 and 2001, which was required to reverse its slump and keep the tower upright.

It means the building in Tuscany, which attracts thousands of tourists every day, is back to the tilt it had at the beginning of the 19th century, according to professor Salvatore Settis, who leads the surveillance group of the monument.

“The reduction of the tilt will not last forever — but it’s very significant and now we have good reasons to hope that the tower can last for at least another 200 years,” Settis told CNN.

When corrective work began on the tower it was leaning six degrees, or 13 feet, off the perpendicular on its south side. Soil was removed on the opposite side in order to reverse its trajectory.

“Technically it has been an incredibly complex work — but the concept of the project is easy to understand,” Settis said. “The tower is leaning towards the South, so part of the soil under the northern side, basically sand and clay, was eliminated, creating cavities that the weight of the tower is now closing.”

The operation forced the closure of the Tower to visitors for nearly a decade. It was reopened in late 2001.

Pisa’s most famous landmark began sinking into its surroundings almost immediately after being erected.

Construction of the tower started in 1173 in the then-seafaring republic of Pisa, but the sandy soil meant it quickly began its tilt.

This latest measurement shows the good health of the monument, according to Gianluca De Felice, director of the Opera della Primaziale Pisana, the institution in charge of the complex of monuments on the Square of Miracles.

“We can express cautious optimism,” De Felice said.

The tower is constantly monitored, and the data are examined by a surveillance committee which meets every three months.