Marcia was the legendary third female ruler and a regent of the Britons, as recounted by Geoffrey of Monmouth.
[2] Marcia became Queen consort when she married Guithelin[3] (Welsh: Kyhylyn) and ruled as regent for her son, Sisillius II.
[4] Geoffrey says that Queen Marcia was a learned woman who codified the Marcian Laws, the Lex Martiana.
King Alfred the Great was later to translate the code into Old English as the basis of Mercian Laws, believing them to have been named after the much later Saxon kingdom of Mercia.
[1][4] Sisillius (Welsh: Saessyllt), came to the throne in ca 358 BC on Queen Marcia's death.