Like so many other early Christian churches, Santo Stefano Rotondo was built on the land of a patrician family whose members had converted. And like so many other early churches, it was also built on the foundations of a previous place of worship, in this case a Mithraeum (spaces in which the Middle-Eastern cult imported by the Roman legions was practised).
Unlike so many other early Christian churches however, this one was custom built from scratch, as opposed to having been an already existant building (such as a domus or gov’t basilica) subsequently converted for worship. Also, unlike most other early churches, it was built.. well.. rotondo (i.e. in the round).
It is supposedly modeled after the Rotunda of the Holy Sepulchrein Jerusalem, and was dedicated in the mid-5th century to Saint Stephen whose remains had just previously been found in the Middle-East and brought to Rome.
Already majestic enough with its 22 enormous inner columns and 44 outer ones, it must originally have been even more impressive with yet another outer ring of arches, now gone. The effect of its shape and the concentric rings of columns upon your entering the church is unique, as nothing from the outside prepares you for the unusual use of space and play of light that you will encounter inside. A must-see!