Welsh law was a form of Celtic law with many similarities to the Brehon law of Ireland and particularly the customs and terminology of the Britons of Strathclyde. It was passed down orally by jurists and bards and, according to tradition, only first codified during the reign of Hywel Dda in the mid-10th century. The earliest surviving manuscripts, however, are in Latin, date from the early 13th century, and show marked regional differences. The law is only known to have been revised by a few rulers (particularly Bleddyn ap Cynfyn, who was credited with revisions retained in the kingdom of Powys) but was obviously updated by jurists in response to changing jurisdictions and circumstances, so that the surviving manuscripts cannot be considered an accurate portrayal of Hywel's first code.