El Cantar de Mio Cid is a 12th-century Spanish epic poem that tells the story of Rodrigo Díaz de Vivar, known as El Cid. The poem narrates his journey from exile to becoming a national hero, highlighting themes of honor, loyalty, and the struggle for justice. The work is divided into three parts, detailing El Cid's battles, his relationships with his family, and his eventual reconciliation with the king. It is one of the earliest examples of Spanish literature and reflects the historical context of the Reconquista, the period of the Christian conquest of Muslim territories in Spain.