A final theory posits that the Percheron and the Boulonnais breed are closely related, and that the Boulonnais influenced the Percheron when they were brought to Brittany as reinforcements for the legions of Caesar. It is known that during the 8th century, Andalusian stallions were crossed with mares native to the area, and more Oriental horse blood was introduced by the Comte du Perche upon his return from the Crusades and expeditions into territory claimed by Spain. Further blood from Spanish breeds was added when Rotrou III imported horses from Castile.[7] No matter the theory of origin, breed historians agree that the terrain and climate of the Perche area had the greatest influence on the development of the breed.[8] A possible reference to the horse is made in the 13th-century romance Guillaume de Dole, in which the title character asks for "the Count of Perche's horse" to be made ready, possibly indicating the "'great horse,' which could accommodate an armored knight" and was bred in the geographical setting of the poem.[9]