After years of war (starting with the titular Sicilian Vespers in 1282), in 1299 an alliance of Angevin, Aragonese, and papal forces began to conduct a successful land campaign on the island of Sicily.

Led by Aragonese–Sicilian admiral Roger of Lauria and Angevin prince Robert of Anjou, the allied army moved throughout eastern Sicily, attacking cities and towns in an attempt to erode Sicilian resistance.

As part of the plot, di Sosa convinced a prisoner (a French noble named Charles Morelet, who had been captured at Falconaria in November) that he wished to defect to the allied cause, citing his desire to remain loyal to the pope.

The noble was then allowed to leak news of di Sosa's alleged defection to Robert, to whom the supposed defector offered to open the gates of the castle of Gagliano.

Robert received the intelligence and summoned a council of war to discuss a plan to seize Gagliano; the castle was a tempting target, as it was located close to Frederick's Sicilian army headquarters in Enna.