What is the theme in El Cid ?

Nobility and class are themes. An epic about a highly successful social climber, the Cantarde mio Cid has much to say about the concept of nobility. For example, the Infantes de Carritfn are characterized as members of the upper nobility; they have vast land-holdings and enjoy high status in King Alfonso's court. They marry the Cid's daughters for their money, but later describe these marriages as "concubinage," implying that this match is null and void because of the vast difference in class between the Infantes and the Cid, According to medieval Spanish law, those of illegitimate birth cannot legally marry, and can only be concubines, rather than legitimate wives.