What is special about the Tower of Pisa?
The structure in Pisa, Italy is famous for the settling of its foundation, causing it to lean 5.2 metres from the perpendicular. The bell tower was built in 1174 as the third and final structure of the city's cathedral complex. It was designed to stand 56 metres and was constructed in white marble.
Three of its eight storeys were completed when the uneven set tling of the building's foundation in the soft ground became noticeable.
Bonnano Pisano, the engineer in charge, sought to compensate for the lean by making the new storeys slightly taller on the short side. But the extra masonry caused the structure to sink even further. Work was suspended several times as engineers sought solutions, but the tower was ultimately topped in the 14th century, still leaning.
What is a barrier reef?
It is a line of corals roughly parallel to a shore and separated from it by a lagoon or other body of water. A barrier reef is usually pierced by several channels that give access to the lagoon and the island or the land beyond it.