Believe it or not the Leaning Tower of Pisa was not designed to lean. Construction began in the 1173 and completed until 1372! That’s a whopping 199 years!Very early on the engineer realized that the tower was beginning to lean, and despite their best efforts the tower continued to tilt as the build continued.
Over time the tower’s tilt increased at an average rate of 1mm every year. 1mm doesn’t sound by much but by the 1990 the tower was at risk of toppling over it was closed to the public.Engineers over the years had different ideas on how to stop it falling over. One such idea did more damage than good and is commonly known as Black September.In September 1995 architects decided to attach 10 steel weights 45 meters underground and pump in liquid nitrogen to freeze the soil.
The idea was good enough but during installation the tower suddenly started leaning even more. Engineers immediately piled any heavy objects they could find to stop it falling! Source: BBC Earth Lab