María Díaz I de Haro

She was the daughter of Lope Díaz III de Haro who was assassinated by order of the king at Alfaro, La Rioja.

On June 8, 1288, her father was assassinated in Alfaro by order of King Sancho IV of Castile over a deep seated disagreement between the two parties.

Maria's husband, John, who was also the brother of Sancho IV and one of the infantes of the Kingdom of Castile, was also present during the episode and was thrown in prison for his role in the affair.

Diego Lopez V found almost no opposition to his initial takeover of Biscay in large part due to the fact that Maria's husband, the infante John of Castile, was in prison for offenses related with her father's cause against Sancho IV.

Once freed from prison, John of Castile immediately set to work attempting to regain control over Biscay.

Eventually, John and Maria were able to successfully gain a claim of legal title to the Lordship of Biscay from the Pope.

In 1307, during a general meeting of the court of Biscay, Diego the intrusive was obliged to recognize Maria as the legal heiress to the lordship and asked her to accept the title to be conferred after his death, an event which occurred in 1309.

As a result, Maria Diaz I remained in her capacity as Lady of Biscay and head of the House of Haro.

The Castilian forces were obliged to retreat some 15 kilometers from the city at Cerro de los Infantes, Pinos Puente.

Juan de Haro sought to expand the influence of the lordship of Biscay, contracting marriage with the niece of the king of Aragon.