The Marques de Mancha had marched quickly. Even when the Duque de Catalonia recieved his new orders, Mancha had already left a siege force behind in Catalonia, and was moving on to Gerona. The French, lending what aid they could, had moved on Rousillon. Catalonia, finding that he was running out of places to fight them, decided to try and beat Mancha to Gerona, so as to defend on home ground. Catalonia would fail to arrive in time, and by October 30th, Mancha had Gerona under general siege.
But Catalonia was only a day behind him, and on December 1st, he marched his army of 38,000 peasant footsoldiers onto the plains of Gerona. Facing the noble duque was 36,000 of Mancha's knights.
Mancha knew the sorry state of Catalonia's forces, and he planned accordingly. During the night, his men harassed the Aragonese. No real fighting took place, but between insults, taunts, the throwing of animal dung, and general mayhem being caused, Catalonia's tired men got no rest.
When the dawn broke, Mancha formed his men into battle lines. He rode before them, riding up and down the front of his lines, raising the spirits of his men and urging them to victory. He reminded them, "What would you do if your daughters were treated like the queen was by this lecher, Ferdinand? Well, think on that as you ride into the ranks of these vile creatures!"
Catalonia formed his men up as well, facing the enemy as best he could. Since he had no cavalry, he could do little more than wait for the enemy to charge. Mancha, wanting to clear the pig-dogs from the field, obliged him quickly.
Mancha's knights charged them from behind.
With no cavarly screen, Catalonia had no way of knowing that the majority of Mancha's men had rounded behind him during the night. The result was that hopes of Ferdinand were crushed on the fields of Gerona on that day. Within an hour, his men fled even as Mancha's knights cut them down.
Catalonia personally refused to retreat. Throwing off his armor and shield, he gripped his sword, taunting the Castilians to fight him like man. Mancha, not wanting to give him the satisfaction of a warrior's death, trampled him unceremoniuosly with his horse.
On December 1st, the Battle of Gerona saw complete land victory for Castile. All Iberian possesions of Aragon would face Mancha's sieges.