The Vendée Royalist forces were well protected in defensive positions, but were divided into separate armies. Suzannet occupied the heights of Rocheservière, protected to the west by the
Boulogne river, which was difficult for an army to cross. Another force under Bertrand Saint-Hubert was in
Saint-André-Treize-Voies, nine kilometers east of Rocheservière. As for Charles Autichamp, he was positioned Vieillevigne north-east, 7 kilometers from Rocheservière and 4 km from Saint-André. These positions would be difficult for the Bonapartists to attack, but on 19 June Suzannet's force suddenly withdrew from Rocheservière and occupied Mormaison to the south east. The Bonapartists took the opportunity to launch an attack on the Vendeans. The
chasseurs under
Jean-Pierre Travot clashed with the Vendeans at La Grolle between Rocheservière and Saint-André. However Suzannet's cavalry were sent in, forcing Travot to retreat. Suzannet then brought all his troops up to La Grolle. The next day, 20 June, Suzannet decided to meet the Bonapartists in battle. He wrote to Autichamp, the commander in chief, asking him to join him, but Autichamp refused to move immediately saying he was securing his position. Suzannet and Saint-Hubert then crossed the Boulogne river and marched to meet the Bonapartists. The two armies met on the moors of the Grand-Collet, South West of Rocheservière. The separate forces of Saint-Hubert and Suzannet were at some distance from each other. The Bonapartists under Travot first entered into contact with the forces of Saint-Hubert. Saint-Hubert's men were taken in the flank by Travot's chasseurs, and were routed. Suzannet arrived too late to retrieve the situation. Seeing the rout of Saint-Hubert, he launched a desperate charge at the Bonapartist lines. In the ensuing fight Suzannet collapsed, seriously wounded by a bullet. Lamarque then ordered his cavalry to attack, and Suzannet's forces broke and fled the field. At Vieillevigne, General Autichamp was informed of the fighting at Grand-Collet. He immediately marched towards Rocheservière, but only arrived in time to witness the rout of Suzannet and Saint-Hubert. Autichamp then decided to place his men in defense of the bridge over the Boulogne. But Lamarque forded the river, taking Rocheservière, and moved round behind the Vendeans. They panicked and fled, falling back in disorder to the north of Clisson. The next day General Suzannet died of his injuries at
Aigrefeuille-sur-Maine. ==Aftermath==