The theater used three architectural styles for the tiers: the doric order columns for the first (bottom) tier and ionic order for the second. It is believed that corinthian style columns were used for the third, but we cannot know for sure since that tier had been removed.
In the 11th and 12th centuries CE, the theater was used as a fortress by the Pierleone family. The fortified walls built around/on it actually helped preserved the building at the time.
Alterations were made and apartments were added in the early 1700s by the Orsini family. This is the reason the theater now has only two of the original three tiers of arches.
Works Cited
"Theater of Marcellus." Rome Reborn. N.p., n.d. Web. 22 Mar. 2017.
"Theatre of Marcellus." Ancient History Encyclopedia. N.p., n.d. Web. 22 Mar. 2017.
"Theatrum Marcelli." LacusCurtius • The Theatre of Marcellus (Platner & Ashby, 1929). N.p., n.d. Web. 22 Mar. 2017.
Page by William Wenstrand and Garin Jankowski