A continuous aisle around a circular building, or a semi-circular aisle curving around the apse of a church behind the main altar. Developed during the Romanesque period, it made it easier for large religious processions to move about inside the church. The addition of the ambulatory led to the construction of radiating chapels, each with its small altar for worship. Also, it may refer to a covered walkway outdoors, as in a cloister.