“Red Phaedrus” from “Mark of the Horse Lord” by Rosemary Sutcliff.
For the Sutdliff Swap 2012.: http://archiveofourown.org/collections/sutcliff_swap2012/works/479165
The story, set in Scotland just beyond the reach of the Roman Empire in 2 AD, has overtones of The Prisoner of Zenda, with Phaedrus, an ex-slave and gladiator, masquerading as Midir the long lost king of the Dalriada. He is described as having hair the colour of hot copper, and is wearing all his royal jewelry. He is standing in front of Dun Monaidh, which is the modern day Dunadd Hillfort.
This was a last minute gift for a Pinch-hit author, and was a very quick and sketchy painting by my standards.