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.
Wikimedia Commons

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]

References

  1.  
  2. p. 168

Bibliography

Cherry, B. “Ecclestical Architecture.” The Archaeology of Anglo-Saxon England, edited by David M. Wilson, Cambridge University Press, 1981.
Curl, James Stevens, and Susan Wilson. “Porticus.” The Oxford Dictionary of Architecture, 4th edition, Online, Oxford University Press, 2021, https://www.oxfordreference.com/view/10.1093/acref/9780191918742.001.0001/acref-9780191918742-e-5885.