See caption
Plan of St Mary’s Church, Reculver, in north-east Kent. The porticuses of the 7th-century church are represented by the blue extensions to the north and south of the original structure, which is shown in yellow; other colours represent other later additions.
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Porticus is a term usually used to describe the side chambers typically added to the north and south sides of an early Christian church, giving the structure an overall cruciform plan.[1]

This architectural feature of church design emerged during the late Roman period, and continued to be used in churches built in Anglo-Saxon England until the 8th century.[2]