Their form is similar to that of the theatres. They have a central space where the spectacles take place, around which there is the seating area. The most essential difference is that usually the odeia are roofed.

From the first odeion of ancient times, the Odeion of Pericles, which is the only odeion of Greek antiquity, until the subsequent Roman odeia, their architecture constantly evolves, and as a result there is no specific or standard architectural type. Thus, the Greek odeion of the Classical period with the square plan and the several columns supporting the roof is succeeded by the first rectangular Roman odeia -which resemble to theatres in the interior- and then by the semicircular odeia with the parts of the theatre: the cavea, the orchestra and the skene.

General view of the Roman odeion of Nicopolis, 1st century A.D.

The evolution of the odeia demonstrates an effort to improve the visual and acoustic conditions, in order to serve many functions. Indeed, while the Odeion of Pericles was mainly used for music events the Roman odeia hosted various spectacles, such as lectures, poetry recitations, mimes and pantomimes. They also functioned as spaces for the gatherings of the members of the assembly. The use of the odeia was not always separated from that of the theatres, as many times they both hosted the same spectacles. It seems though that the odeia were suitable for high quality events so they were addressed to the high society of the city.