The Black Sheep. Catalan Chronicles, #1

Constantinople 1302. Luca Baldi, a young shepherd, is catapulted into the violent world of mercenary warfare when he is forced to flee his native Sicily. He falls in with the Almogavars - ruthless mercenaries from the Catalonia region of Spain who have just finished butchering the French during a 20-year war on the island. He and they take ship to Constantinople when they are hired by the Byzantine emperor, whose empire is disintegrating in the face of remorseless Muslim advances.
Alone and marooned amid danger and violence and surrounded by enemy forces, Luca must master the Almogavar way of war to survive. Plunged into the brutal world of Medieval warfare when the mercenaries take the fight to the emperor's many enemies, can Luca live through fighting impossible odds as he battles to preserve a crumbling empire that has stood for a thousand years?'The Black Sheep' is the first volume in the Catalan Chronicles, a Medieval saga set in the early 14th century.