But there fortune changed.

The presence of foreigners and Christians on the soil of Spain caused a suspension of interior quarrels amongst the Arabs, who rose in mass, at all points, to succor Saragossa.
The besieged defended themselves with obstinacy; there was more scarcity of provisions amongst the besiegers than inside the place; sickness broke out amongst them; they were incessantly harassed from without; and rumors of a fresh rising amongst the Saxons reached Charlemagne.

The Arabs demanded negotiation.

To decide the king of the Franks upon an abandonment of the siege, they offered him "an immense quantity of gold," say the chroniclers, hostages, and promises of homage and fidelity.
Appearances had been saved; Charlemagne could say, and even perhaps believe, that he had pushed his conquests as far as the Ebro; he decided on retreat, and all the army was set in motion to recross the Pyrenees.
On arriving before Pampeluna, Charlemagne had its walls completely razed to the ground, "in order that," as he said, "that city might not be able to revolt." The troops entered those same passes of Roncesvalles which they had traversed without obstacle a few weeks before; and the advance-guard and the main body of the army were already clear of them.
The account of what happened shall be given in the words of Eginhard, the only contemporary historian whose account, free from all exaggeration, can be considered authentic.

"The king," he says, "brought back his army without experiencing any loss, save that at the summit of the Pyrenees he suffered somewhat from the perfidy of the Vascons (Basques).