Interior of Santa Costanza, Rome, c. 350, Photo by Oliver-Bonjoch via Wikimedia Commons,  Creative Commons Attribution-Share Alike 3.0 Unported license. © 2013 . All rights reserved.

Just a Second: Ambulatory

Ambulatory (noun)

A place for walking, usually an aisle in a church around the apse.

In Santa Costanza in Rome, the mausoleum for the Roman Emperor Constantine’s daughter Constantina, the ambulatory is circular and goes around a space where the sarcophagus of Constantina originally stood.