The Column of Trajan, completed in AD 113, stands 40 m (131 ft) high. A spiralling band of superbly carved reliefs tells the tale of Trajan's Dacian Wars. There are very small windows in the column, which allow just enough light inside to light up the spiral staircase which spirals up the inside.
The column owes much of its survival to the papacy. Pope Gregory the Great was moved by a scene depicted on the column which showed Trajan aiding the mother of a dead soldier. And so he prayed for Trajan's soul to be spared. The tale goes on to say that god spoke onto Gregory that Trajan indeed had been saved from hell, despite his pagan life.
So kindly disposed was the church to one of Rome's greatest leaders that his statue remained atop the column for a very long time. It was only in 1587 that his statue was finally replaced by one of St.Peter.