The combat of San Giorgio (20 June 1799) was a rear-guard action during the French retreat after their defeat at the battle of the Trebbia (17-19 June 1799). At the end of that battle General Macdonald retreated to the line of the Nura River, which flows north from the Apennines to the Po, joining that river just to the east of Piacenza.
Marshal Suvarov, commanding the combined Austro-Russian army, was determined to prevent the French from escaping across the Apennine Mountains. The pursuit began at four in the morning. Suvarov was greatly encouraged when his scouts captured an emissary from Macdonald to General Perignon in which he detailed the disorder of the French army and the direction of their retreat.
The Russian advance-guard caught up with General Victor's column at a ford near to San Giorgio on the Nura. For some time six squadrons of French cavalry and two cannon were able to defend the ford, but they were pushed back when General Bagration arrived with reinforcements. Victor then decided to retreat from San Giorgio, leaving a demi-brigade from the 17th Line to hold the village. This force managed to delay the Allies for some time, but eventually two fresh Russian divisions arrived, crossed the river above and below the village and trapped the French. Only 400 men escaped.
This rear-guard action gave the rest of Victor's men time to retreat. Some moved north-east towards Cadeo, where they joined the French right, while others moved south-east towards Castell Arquato, on the edge of the Apennines.
Further north Piacenza fell to the Allies at six in the morning. General Watrin, commanding on the French right (nearest the Po), held the line of the Nura until he was forced to pull back by Victor's retreat. Watrin retreated east to Cadeo, and then to Fiorenzola. The French artillery parks were nearly lost to the Allies, before being saved by a single demi-brigade which escorted them to Cortemaggiore, just to the north of Fiorenzola.
Macdonald continued to retreat east, winning a key combat at Sassuolo on the Secchia River on 23 June. This allowed him to slip away to the south, cross the Apennines, and then advance west along the coast to join up with General Moreau at Genoa.