It is believed that the Asinelli Tower initially had a height of ca. and was raised later to the current , with an overhanging battlement of 2.2 m (6.6 ft). In the 14th century, the city became its owner and used it as a prison and small stronghold. During this period, a wooden construction was added around the tower at a height of roughly 30 metres, about 100 feet, above ground, which was connected with an aerial footbridge to the Garisenda Tower. The footbridge was destroyed in a 1398 fire. Its addition is attributed to
Giovanni Visconti,
Duke of Milan, who allegedly wanted to use it to control the turbulent
Mercato di Mezzo, the central street, today the via Rizzoli, to suppress possible revolts. The
Visconti had become the rulers of Bologna after the decline of the
Signoria of the
Pepoli family, but were rather unpopular in the city. Severe damage was caused by lightning that often resulted in small fires and collapses. In 1824 a
lightning rod was installed. The tower has survived at least two documented large fires: the first in 1185 due to
arson and a second in 1398. The Asinelli Tower was used by the scientists
Giovanni Battista Riccioli in 1640 and
Giovanni Battista Guglielmini in the 1700s for experiments to study the motion of
heavy bodies and the
Earth's rotation. In
World War II, between 1943 and 1945, it was used as a sight post: during bombing attacks, four volunteers took posts at the top to direct rescue operations to places hit by
Allied bombs. Later, an
RAI television relay was installed on top. ==Garisenda Tower==