500-600 FALSE - I had to look this one up, because I thought Offa's Dyke was built later than this, and it must have been. His dates as 757-796. First King of Mercia was Creoda (585-593), followed by Pybba (593-606). Offa did build the dyke, but later than 500-600.

Going to investigate now whether there had been some natural/man-made division prior to Offa's Dyke, that he then added to.

Thanks for these questions, Ian C !

- jeanie