The chief narrative source for the siege of Bayonne is the Chronica Adefonsi imperatoris, a contemporary account of events in Spain compiled to celebrate the feats of Alfonso VII of León and Castile.

In March that year, with Suero Vermúdez, he had even taken the capital city of León from some rebels holding out in favour of an illegitimate half-brother of Alfonso VII, one of the sons of his mother, Queen Urraca, and her lover, Pedro González de Lara.

In besieging Bayonne, Alfonso the Battler was perhaps hoping to persuade the Count of Toulouse to switch allegiance to him and aid him in his war in Castile.

[3] The attacking army was probably already passing through the Pyrenees when, on 4 September 1130, Alfonso visited a chapel in Ardanés, a now depopulated village in the Valle de Hecho.

[6][7] According to the Chronica, "during the time when Alfonso was at war with the rebel nobles ... the King of Aragon had mobilised sizeable armies of knights and infantrymen ... had traveled then beyond his own borders to Gascony [where] he surrounded the city of Bayonne which is located near the Garonne River.

"[8] It subsequently relates how for several days he plundered the countryside around Bayonne before assaulting the city's walls with siege engines brought from Aragon.

In the words of the Chronica: "Count Pedro asked the Count of Toulouse for single combat" (comes Petrus petiit comiti Tolosano singulare certamen), "both went out to fight much like two strong lions" (sicut duo leones fortes), and "Count Pedro was wounded by Alfonso's lance and, falling from his horse, broke his arm and died a few days later" (et vulneratus est comes Petrus ab hasta comitis Adefonsi et, cadens de equo, fractum est brachium eius et post paucos dies mortuus est).

The siege continued through the summer, but in July and August Alfonso was leading forces in a place called Rocha Tallata or Rocathalada, possibly modern Peyrehorade.