Pausanias identifies the roofed theater that dominated the Agora as the Odeion of Marcus Agrippa.   This building has been firmly dated to the end of the first century B.C.E.  Various pottery deposits discovered in the foundations, surviving architectural members, and even technical similarities in construction techniques to other buildings erected at the same time all point to a date during the Augustan era.   Also, the building’s expense and Philostratos’ reference in the Vitae Sophistarum to the "Agrippeion" (2.5.4 and 2.8.3-4) further place the building’s erection during Marcus Agrippa’s visit to Athens, between 16 and 14 B.C.E.   Indeed, Agrippa was given a very conspicuous dedication at the entrance of the Acropolis Propylaea by the Athenians at this period.   Many scholars believe the Agrippa Monument was a response to his gift of the Odeion.

The bulky form of the Odeion, stylistically foreign to Athens but similar to auditoriums in southern Italy,  dwarfed the landscape of the Agora and was wholly out of place in its proportions and its placement.  The space now occupied by the building was formerly part of the market square and had been the site of the Orchestra from the sixth to the fifth century B.C.E.   The site of the Orchestra had long been revered by the Athenians and was significant in its selection for the site of the new building.   Once the Theater of Dionysus was constructed, fewer performances were held at the Orchestra but the area, still retained the older associations.  The old marketplace was replaced by the new Agora of Caesar and Augustus; the construction of the two buildings overlapped, and the empty area left in the Agora was transformed into a space very similar to that of contemporary Roman imperial fora.   The Odeion encroached on space that had been maintained without buildings since the Archaic period.  The only exception through that long period was the statue group depicting the Tyrannicides.

The reasons behind the construction of the Odeion are somewhat contradictory.  The Odeion of Pericles on the south slope of the Acropolis had been renovated only about fifty years earlier by Ariobarzanes Philopater (65-52 B.C.E.) and was surely still in use.   Yet the numerous columns of the older Odeion obstructed the view.  The erection of a music and lecture hall in the middle of the Agora would serve as a grand monument remembering "a city where sophists and philosophers had replaced generals and orators as the most notable citizens."   The lavish use of marble and the grandeur of such a monumental structure must have reminded the Athenians of the great days of their own culture.  But it also served as a focus of the Agora landscape where, in performances and in the surrounding structure itself, Romans and other peoples of the empire could revere the Athenians’ ancestors,  who were morally and intellectually superior to the Athenians of their own day.

The placement of the Odeion in the middle of the Agora might have also had another effect. Along with the Temple of Ares, the two buildings could be seen "as a deliberate disruption of civic activities in (their) new setting."   The Altar of Zeus Agoraios also was moved at some point during the end of the first century B.C.E. from the Pnyx to a space to the east of the Metroon.  Once the Athenian Agora was filled with religious and cultural monuments, the civic role it had formerly filled was no longer as prominent to the tourist or even to the Athenians themselves.

The similarities of the Odeion to other Roman projects in Attica at the time, especially the repairs on the Erechtheion, have been emphasized, most notably by H.A. Thompson.  Even before a Corinthian capital found at the site was suspected to have been from the Odeion, a thorough analysis placed its creation shortly after the date provided by similar capitals from the Inner Propylaea at Eleusis (begun 50-48 B.C.E.).   The mouldings of the architrave, frieze, and cornice of the Odeion’s main order are also similar to those found in the Tower of the Winds and the Market of Caesar and Augustus.   The Market of Caesar and Augustus also has another tie to the Odeion in that technical similarities, such as the use of certain clamps and cutting styles, are "so close, as to leave little doubt that the two building programs were in progress at the same time."   Not only do certain classicizing features of the Odeion reflect upon contemporary building techniques and the revival of interest in the architecture of the Erechtheion, but the window arrangement of the Odeion may well have been inspired by the classical Greek lighting method used in the Erechtheion.  The interiors of both buildings are illuminated by indirect lighting; that is the interior rooms were mainly lit by reflected light from intermediate rooms.  Also, the windows created in the Erechtheion’s west cella wall (ca. 25 B.C.E.) are closely imitated in those of the Odeion.