Excavations begin this weekend at the remains of an ancient Saxon rotunda discovered in Herefordshire last month.
The 1,000-year-old round church, in Leominster, is thought to be part of a Saxon monastery founded by one of Britain's ancient rulers.
The dig is taking place at Grange Court, on land currently used as a car park by council staff.
Archaeologist Bruce Watson said the remains were expected to be the best preserved of their type in the country.
He said: "This is an important find and it could be an opportunity to re-write the early history of Christianity.
"Obviously it is difficult to predict at this stage just what condition the rotunda building is in and how spectacular the remains will be to the naked eye."