This positioning allowed the town of Agoncillo to control the passage of these rivers and oversee the important road running through the area.

The current town is believed to occupy the site of the ancient and now ruined settlement of Egón, from which it derives its modern diminutive name.

[3] The theory of its Roman origins is further supported by the presence of a documented road that passed nearby, an important route during the Middle Ages.

They later transferred the town to the Monastery of San Juan de la Peña in exchange for a horse and ten oxen.

In the sentence given by Henry I of England, the right bank of the Ebro was assigned to Castile, making Agoncillo a crucial frontier defense.

[4] In 1182, Alfonso VIII expelled the Navarrese from Agoncillo and Arrúbal, indicating a repopulation effort to strengthen the frontier.

This act ensured the continued prominence of the Medrano family in Agoncillo, which remains renowned for its reverence toward the humble saint of Assisi.

[6] The Medrano family generously donated some land, including a tower, situated close to the Ebro River within the city of Logroño as a gift to Saint Francis, establishing the first Spanish convent of his Order there.

[7] Unfortunately, despite its centuries-long legacy of glory and sanctity, the convent met its demise in the 19th century due to the advent of liberalism and its accompanying laws.

[8] Alfonso XI of Castile granted the Lordship of Agoncillo to Sancho Sánchez de Rojas and Ursula Díaz his wife on September 1, 1336 in Lerma.

In Rodrigo Alfonso de Medrano's testament in 1345, he noted having spent big amounts of money in "...building the castle and the village" (in Old Spanish "...fazer el castillo e la villa").

[10] During the battles between Peter the Cruel and Henry of Trastámara, the castle passed onto the hands of Charles II of Navarre, although for a short period.

[33] Juan Jerónimo de Frías Salazar Porras y Medrano recorded a book of income, censuses, accounts and rights that he possessed, as lord of Agoncillo.

While the early owners typically resided in Logroño, from the 16th century onwards, their descendants chose to live in Alfaro, where they also held substantial properties.