The construction was very robust: Michele Ferno, an eyewitness of the demolition, could visit the burial chamber, which was reachable through a long tunnel; its walls had four niches to keep the defuncts' ashes, and with a side of 7 m and a height of 10.5 m it was almost as big as that of the Mausoleum of Hadrian (which has a side of 7.8 m and an height of 10–12 m).