The monument is a tetrastyle structure. It has 18 tapered, unfluted columns: seven along the north- and south-facing sides and four facing the east and west. The columns are in diameter, and high. There are two parapeted walkways running from east to west at the top of the monument; the parapets are tall. One column—the second from the east on the south-facing side—contains a 74-step spiral staircase leading to the southern walkway. The columns support a deep entablature, whose serves as the walkways; the columns, and the walls of the foundation and entablature, are hollow. The entablature is made up of the architrave, frieze and cornice; the architrave and cornice are simple in design, and the frieze is adorned with triglyphs, although these are stylised and lack grooves. There is a triangular pediment at each end of the entablature; the total height of the entablature and pediments is .