Italy's tower of Pisa has never stood straight -- it started leaning before workers finished building it in the 1300s! The ground it was built on wasn't strong enough to support a heavy building.
The tower has been tilting a tiny bit each year since it was built. A few years ago, experts worried that it might topple over. In 1990, they closed it and began working on it. They wanted to keep the tower from leaning any more than it already did.
Workers added steel cables and concrete around the base. Then they put heavy bricks on the concrete. The weight of the bricks helped straighten the tower a tiny bit. Next they plan to shift the ground to hold the tower steady. But experts don't want it to stop leaning -- that's what the tower is famous for!
topple -- to fall forward as having too heavy a top.
Pisa -- the name of a famous tower in Italy.
leaning-- to bend from a vertical position.
tilting -- slope.
tiny -- very small.
expert -- a person who has special skill or knowledge
concrete -- a kind of strong building material