St. Peter's Basilica, as it stand today, was begun in 1506. The first basilica, which is now called "Old St. Peter's Basilica" was begun by the Emperor Constantine between 326 and 333 AD. This was a big wide church in the shape of a Latin Cross, over 103.6 metres (350 feet) long. The central part called the "nave" had two aisles on either side, separated by rows of talls Roman columns. In front of the main entrance was large courtyard with a covered walkway all around. This church had been built over a small "shrine" (little chapel) believed to mark the burial place of St. Peter. The old basilica contained a very large number of tombs and memorials, including those of most of the popes from St. Peter to the 15th century.