I'm trying to work out who would be found on coins in England circa 270 AD. Don't have exact dates but I've been told they were Belgian and for a period were trying to stop piracy in the channel. Sorry for being vague, don't have a lot of info but am interested to know more about them if anyone this is true.
Sounds like you're referencing the semi-legendary Carausius. Edit: So these are the coins you might be referring to http://www.forumancientcoins.com/lateromancoinage/carausius/medallions/medallions.html Supposedly Carausius came to power round about 286CE. You might also be refering to one of the rulers of the Gallic Empire, a roman seperatist empire that controlled Gaul and Roman Britain. There were a bunch of them and the dates of their reigns are all jumbled up but they were a think in the 260s and 270s.
In power for 7 years I believe