The pyramid was built about 18–12 BC as a tomb for Gaius Cestius, a magistrate and member of one of the four great religious corporations in Rome, the Septemviri Epulonum. It is of brick-faced concrete covered with slabs of white marble standing on a travertine foundation. The pyramid measures 100 Roman feet (29.6 m) square at the base and stands 125 Roman feet (37 m) high.
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 opened in 1660, the chamber was found to be decorated with frescoes, which were recorded by Pietro Santo Bartoli. Only scant traces of these frescoes survive, and no trace of any other contents. The tomb had been sealed when it was built, with no exterior entrance, but had been plundered at some time thereafter, probably during antiquity. Until the end of restoration works in 2015, it was not possible for visitors to access the interior, except by special permission typically only granted to scholars. Since the beginning of May 2015, the pyramid is open to the public every second and fourth Saturday each month. Visitors must arrange their visit in advance.
A dedicatory inscription is carved into the east and west flanks of the pyramid, so as to be visible from both sides. It reads:
Below the inscription on the east-facing side is a second inscription recording the circumstances of the tomb's construction. This reads:
Another inscription on the east face is of modern origins, having been carved on the orders of Pope Alexander VII in 1663. Reading INSTAVRATVM · AN · DOMINI · MDCLXIII, it commemorates excavation and restoration work carried out in and around the tomb between 1660–62.
At the time of its construction, the Pyramid of Cestius would have stood in open countryside (tombs being forbidden within the city walls). Rome grew enormously during the imperial period, and, by the 3rd century AD, the pyramid would have been surrounded by buildings. It originally stood in a low-walled enclosure, flanked by statues, columns and other tombs. Two marble bases were found next to the pyramid during excavations in the 1660s, complete with fragments of the bronze statues that originally had stood on their tops. The bases carried an inscription recorded by Bartoli in an engraving of 1697:
This identifies Cestius' heirs as Marcus Valerius Messala Corvinus, a famous general; Publius Rutilius Lupus, an orator whose father of the same name had been consul in 90 BC; and Lucius Junius Silanus, a member of the distinguished gens Junia. The heirs had set up the statues and bases using money raised from the sale of valuable cloths (attalici). Cestius had stated in his will that the cloths were to be deposited in the tomb, but this practice had been forbidden by a recent edict passed by the aediles.