Upon the death of Alfonso the Warrior, King of Argon, the problem of who would succeed him arose as his testament left the Kingdom of Aragon to military rule. To resolve the conflict his brother, Ramiro II, who was a Benedictine monk at the time, was chosen by the Aragonese nobility to succeed to the throne.

Ramiro married Inés de Poitou by special papal licence and in 1136 the couple produced a daughter; Petronila, the future queen of Aragon. On 11th August 1137 and under great pressure by the nobles and the papacy, Ramiro arranged the marriage of Petronila, who was only five years old at the time, to Ramón Berenguer IV. Ramón was 24 years old, the count of Barcelona and a Templar Knight His noble lineage meant that he could carry the title of prince of Aragon and so assume rule of the kingdom without dishonouring the Aragonese nobility.

According to tradition, this monumental event took place in the Plaza de la Candelera. The union joined Aragon and Catalunya and gave rise to the historic Crown of Aragon, ratified in 1150 with the marriage of Petronila and Ramón Berenguer in the cathedral of Lerida.

The reign of Ramiro II lasted only three years; as soon as the crisis of succession was resolved and the kingdom was in safe hands he abdicated in favour of his daughter, Petronila.