The pyramid was built about 18 BC–12 BC as a tomb for Caius Cestius, a magistrate and member of one of the four great religious corporations at Rome, the Septemviri Epulonum. It is of brick-faced concrete covered with slabs of white marble standing on a travertine foundation, measuring 100 Roman feet (29.6 m) square at the base and standing 125 Roman feet (37 m) high.[1]

In the interior is the burial chamber, a simple barrel-vaulted rectangular cavity measuring 5.95 metres long, 4.10 m wide and 4.80 m high. When it was (re)discovered in 1660, the chamber was found to be decorated with frescoes, which were recorded by Pietro Santi Bartoli, but only the scantest traces of these now remain. There was no trace left of any other contents in the tomb, which had been plundered in antiquity. The tomb had been sealed when it was built, with no exterior entrance; it is not possible for visitors to access the interior. http://en.wikipedia.org/wiki/Pyramid_of_Cestius