Why does the Leaning Tower of Pisa lean?

 Why does the Leaning 

Tower of Pisa lean?

The tower of Pisa, 58.4 m (192 ft) high,

started to lean soon after building began,

in 1174. Five years later, when stone-

masons reached halfway, money ran out

and work stopped. It was a good job it

did. Studies show that, had building con-

tinued, the tower would have collapsed.

In its early stages, the tower leaned to

the north. Masons varied the marble

blocks in a bid to correct the fault, which

got worse as they went higher. On the

first storey's north side, the blocks are

1 cm (0.4 in) thinner than those on the

south; on the fourth storey, they are

10 cm (4 in) thinner.

Building restarted in 1272, by which

time the tower had almost straightened.

But now it began to lean to the south. Atthe seventh storey, work stopped for

about eighty years. Again, the delay wa

fortuitous. In a final bid to straighten th

tower, the bell chamber was built out o

line. Four steps lead to it on the nort

side and six on the south

Today, the tower still leans to the south

where it is 2.5 m (8 ft) lower than on th

north. For a structure weighing 14 45

tonnes, its foundations are inadequate

just 3 m (10 ft) deep. Also, the soil to th

north has more sand. To the south it i

richer in silt. This compresses more easily

allowing the tower to sink on that side

Over the years, almost every move t

correct the tilt has worsened it. In 1934

Benito Mussolini, the Italian dictator, trie

to save the tower. Engineers poure

tonnes of cement into 361 holes drille

in the foundations. That year the towe

lurched more than in the previous fifteen

In 1989, a similar but upright tower a

Pavia collapsed. The Italian governmen

closed Pisa's tower, and set up an interna

tional commission to stabilise the building

Some twenty years earlier, engineer

discovered that the tower moves hour byhour, reacting to the warmth of the Sun.

Recently, electro-levels - highly sensitive

detectors were installed in the founda-

tions. These showed that as the tower

warms up it rocks its foundations, increas-

ing its tilt. Since the end of World War II,

the rate of tilt has doubled. The tower

leans nearly 2 mm (0.01 in) more each

year, moving closer to the point where it

will topple over.

Some structural engineers fear that

internal stresses may make the building

explode. In 1992, as a safeguard, they

girdled it with eight metal cables. A year

later they loaded the foundations with

600 tonnes of lead.

Suggestions arrive daily from all over

the world. One is to dismantle the tower

and rebuild it straight. Citizens fiercely

oppose the idea. After the tower closed,

tourism fell by 25 per cent. It seems that

everybody wants a leaning tower, pro-

vided it is safe.