The Battle of the Sesia or Battle of the Sesia River, took place near the Sesia River (Latin: Sesites or Sessite), situated in north-western Italy, Lombardy, on 30 April 1524, where the Imperial–Spanish forces commanded by Don Carlos de Lannoy and Fernando d'Avalos, Marquis of Pescara decisively defeated the French army under the Admiral Guillaume Gouffier, Lord of Bonnivet and Francis de Bourbon, Comte de St. Pol, during the Italian War of 1521–1526.
Bonnivet's offensive of 1523
The French army, under Bonnivet, advanced through the Piedmont to Novara, where it was joined by about 18,000 Swiss mercenaries, the best pike-armed infantry available. The French army now comprised some 36,000 infantry (many of whom would be detached from the main force in garrisons) and 2,200 men at arms, plus numerous gentlemen volunteers; there would also have been some light horse but the number of these is not known. Opposing Bonnivet was the Imperial army under Prospero Colonna, who had barely half as many men as the French: only 800 men at arms, 800 light horse and 15,000 infantry.
Colonna, an aging but skilled Condottiere, understood that the key to French success was the occupation of the city of Milan. His best chance of denying the French army its objective was to delay its advance as much as he could, without compromising his own army. Colonna held the line of the Ticino river for as long as he dared but was forced to fall back to Milan on 14 September 1523 when the French began to cross the river in force. Bonnivet paused for a few days to allow his army to rest and regroup. This delay was vital to the successful defence of Milan in two respects: first, the city was stocked with supplies for a siege and protective earthworks were dug; second, with barely two months of the campaigning season left, each day of delay reduced the chances of a siege being effective enough to force capitulation. Had Bonnivet found it possible to vigorously press on instead of resting, the city would have been caught unprepared and was likely to have fallen.
Autumn and Winter Operations, 1523-4
The French laid siege to Milan until mid-November. Then, with no sign of it falling, Bonnivet withdrew his men a few miles to winter quarters at Abbiategrasso. This was to preserve his army from the extremes of disease and privation it was certain to suffer if it remained in its trenches during the winter. Over the next few months, the scales progressively tipped away from the French and towards the Imperials as Colonna's army was reinforced and they were not. In late December, Spanish troops from Naples, led by Lannoy, the Spanish viceroy of that kingdom, and the marquis of Pescara, arrived to bolster Colonna's forces. Any potential for rivalry and dissent over who should command the combined Imperial-Spanish army evaporated almost at once with the death of the ailing Colonna on 30 December, leaving Lannoy as undisputed general. Another reinforcement, this time of 6,000 Landsknechts arrived at the end of January. By now, Lannoy's main problem was not the French but finances: there was no money to pay the army. He warned his political master, Charles V (who was both king of Spain and Holy Roman Emperor), that the army might fall apart through mass desertion unless some funds could be provided; he even suggested negotiating a truce with the French; this would give time to alleviate the problem of pay.
Fortunately for Lannoy, the French were feeling the pressure too. In early February, after Lannoy was reinforced by yet another contingent, this one paid for by Venice, Bonnivet pulled back to a safer position behind the Ticino river. In April, Bonnivet was expecting his own reinforcement of Swiss infantry. However, their arrival actually had the opposite effect on his strength as, when the expected fresh troops arrived, they dropped a bombshell: these Swiss had come only to escort the survivors of the Swiss contingent already with the French army in returning home. At this point, Bonnivet threw in the towel: he decided to end the campaign and head back to France. The army began crossing the Sesia river on 29 April with the Swiss intending to head for home and the depleted French back to France. Bonnivet himself commanded the rearguard, covering the operation. Lannoy saw his chance to harry the retreating French and hastened forward his troops to cause as much damage as they could.
Battle of the Sesia, 30 April 1524
The finer details of the battle, in English at least, are scarce but enough is known of the significant events to recognise its importance.