Of‧fa's Dyke /ˌɒfəz ˈdaɪk $ ˌɔːf-/
a long wall of earth, originally over 100 miles long, put up to mark the border between Wales and the Anglo-Saxon kingdom of Mercia, by King Offa of Mercia in the 8th century. Parts of it can still be seen.

[TahlilGaran] Dictionary of Contemporary English ▲