It is 37mt. high, built in imitation of the Egyptian pyramids, that were in fashion in Rome after the conquest of Egypt (30 to C.).
It is built of a very firm composition of mortar and small stones faced with tablets of white marble.
The original entrance was effected by means of an inclined shaft about halfway up the northern side of the Pyramid.
This shaft (opened in the '600's, when the Pyramid was brought to light), covered outside with a stone, led straight to the centre of the vault, covering the grave-chamber.
The interior walls were decorated with stuccoes and fresco paintings divided in panels by means of painted candelabra that frame female figures (badly preserved).
In the III century the monument was incorporated in the Aurelian Walls.