Built as his own burial place by Theodoric in 520 A.D., the mausoleum, with a central plan, is made of white stone blocks and is divided into two superimposed orders, both decagonal.
Scholars tend to believe that the lower floor was used as a chapel and that the porphyry basin containing his mortal remains would have been placed on the second floor which, already at that time, could only be reached from the outside.
Above the mausoleum stands a large monolithic dome of remarkable dimensions: 10.76 m in diameter and 3.09 m in height.
According to more recent calculations, it weighs 230 tons and, to this day, scholars have advanced a number of hypotheses concerning the transport of the monolith and the technique employed for its installation. On the handles carved out from the monolith, the names of the 4 evangelists and 8 apostles can be read.
Inside, light is provided by six windows, which are all different from each other.
The remains of Theodoric, probably kept here, were removed and dispersed during Byzantine rule, when, following Justinian’s edict in 561, the mausoleum was transformed into an oratory and consecrated to Orthodox worship.