This is the partially restored building at the north end of the square. It had four facades and on each of these were semicircular niches linked to each other by arches on which stood blocks with reliefs on them.
The high reliefs at the foot of the arches are in the shape of caryatids. Reliefs of soldiers in togas are of Memmius, his father Caicus, and his grandfather the dictator Sulla. On the fragment of the architrave lying today near the building is written "Caius Memmius, the Saviour, son of Caicus, grandson of Cornelius Sulla". The monument was built in the 1st century AD.
To the west of the Memmius monument and adjacent to it is a fountain which was built later. The fountain had four Corinthian columns and a long narrow pool. On four bases in front of the pool stood the statues of Diocletian, Maximian, Constantius Chlorus, and Galerius (293-305) who were also emperors of Rome. These statues indicate the date of the building. Similar statues stood also in front of the Temple of Hadrian, a favourite building of the Curetes Street below.