1 Prof. Jones: I was looking through Malory, and cross referencing with The Domesday Book, Geoffrey of Monmouth, and some other sources.
2 Prof. Jones: I've unearthed some leads I think we should investigate.
2 Monty: Oh?
3 Prof. Jones: Yes. In the field, as it were. A trip to old Albion. In search of a certain sword…
4 Monty: Do you seriously think that really exists?
4 Prof. Jones: Well, it's not set in stone.

Sir Thomas Malory compiled or retold the stories of King Arthur and the knights of the Round Table in Le Morte d'Arthur, first published in 1485. This compilation has become the most often used root source for the Arthurian legends - although older sources exist (see below).

The Domesday Book is a record of the surveys of lands and population of Most of England and Wales, which were conducted at the order of William the Conqueror so that the new Norman king would have an up to date reckoning of his lands and the taxes that were due to him. The book was completed in 1086.

Geoffrey of Monmouth was a Welsh cleric who preceded Malory in recording tales of King Arthur. Around 1136 he wrote Historia Regum Britanniae (The History of the Kings of Britain), which was treated for several centuries as an accurate historical record of Britain in the first millennium. Most of it has since been discredited as myth.

According to the legend, Arthur was born in Tintagel Castle, in Cornwall. Unlike Arthur, the castle actually exists - or at least parts of it still do:

Ruins of Tintagel Castle, Cornwall.

Perhaps the Joneses are headed in this direction in the near future...