Towers are some of the oldest things people have built. The oldest known tower may be the circular stone tower in walls of Stone Age Jericho, built nearly 10,000 years ago. Jericho was home to several hundred people, but it still built a massive wall around itself 3.6m/12ft high, and inside it was a stone tower of about the same height, with the top being reached by a staircase of 22 steps. It was the first tower ever to be built, although no one knows if it was a watchtower or a religious tower.
The earliest massive tower in the ancient world was supposed to be the Tower of Babel in Babylon, but this may really have been a religious building, or ziggurat.
Some of the earliest surviving towers are not in the Middle East, but in Scotland. The famous brochs may have been tribal watchtowers and even a place to defend. They are double-walled with a staircase on the inside.
The Romans built many towers, both as watchtowers and for decoration. Hadrian's Wall contains many watchtowers (milecastles and fortlets). The Chinese used towers as guardposts along the Great Wall of China.
The Saxons built watchtowers, many of which have been converted into bell towers of churches. By the Middle Ages, towers were found in all castles, sometimes as a central keep, and also as defensive towers along the walls.
Towers were also built at this time to house bells. The Leaning Tower of Pisa is a cathedral bell tower. Sometimes towers were just built to show who was the most powerful. A competition between rich families started in the Middle Ages in Bologna, Italy, where families built taller and taller towers, just to show who could build taller. They have no other purpose. In the Muslim world towers connected to mosques are called minarets. They were designed to be taller than other buildings so that the faithful would hear the call to prayer.
The tower is square or circular and is a strong shape. This is why it can stand up on its own without its walls being supported. But eventually, the only way to go higher without the tower collapsing under its own weight is to make it tapering.
Towers have also been used as lighthouses since ancient times. One of the Seven Wonders of the Ancient World was the Lighthouse of Alexandria, Egypt, supposedly 130m/400ft tall.
Up to a certain height, a tower can be made with the supporting structure with parallel sides. However, above a certain height, the compressive load of the material is exceeded and the tower will fail. This can be avoided if the tower's support structure tapers up the building.
The tallest modern towers are communications towers. Many cities have one of these. The tallest is the CN Tower in Toronto, Canada, with 147 storeys.
