From Project Athinai
The Odeion (Music Hall), located on the south slope of the Akropolis adjacent to the Theater of Dionysos, was probably a replica of Xerxes' pavilion during the occupation of Athens by the Persians in 480 BC. It was built around 435 BC.
Pericles himself may have been the construction supervisor. The building measured some 62.40 m by 68.60 m and contained several rows of seats, 9 rows of interior columns in the east-west alignment and 10 rows in the north-south alignment for a total of 90 columns. These columns supported its large pyramidal wooden roof. Some authors show the building with solid exterior walls while others argue that it was an open pavilion bordered with columns.
The building was initially erected to host aulos (flute), song and kithara (lyre) contests during the Panathenaia as such it was the first roofed building of the city used for musical contests. Soon, it also served during the proagon (before the contest) of the Dionysia to present the new dramas that would be played at the Theater of Dionysos. The building may also have served as a courtroom and as classroom for the philosophers.
A few years after 421 BC, more precisely in 404 BC, the Odeion was used as a barrack by the 700 Spartan troops stationed in Athens to support the regime of the Thirty Tyrants.
Camp, John M.; The Archaeology of Athens, Yale University Press, 2001, pp. 100-101
Connolly, Peter and Hazel Dodge; The Ancient City - Life in Classical Athens & Rome, Oxford: Oxford University Press, 1998
Hurwit, Jeffrey M.; The Acropolis in the Age of Pericles, Cambridge: Cambridge University Press, 2004
Travlos, John, Pictorial dictionary of Ancient Athens, Books that matter, New York, 1971, p. 387