After service in the Upper Rhine valley and the Netherlands, he joined André Masséna in Switzerland in 1799, and fought at the battles of Winterthur and First Zurich, and Näfels.

Gazan was wounded on 22 November 1796 and taken to hospital in Strasbourg for his recovery, where he met Marie Madeleine Reiss; after their marriage, she frequently accompanied him on his campaigns and they had several children.

[2] On 4 April 1799, his superior and friend André Masséna transferred him to the Army of the Danube, at that time located in the northeastern Swiss plateau.

On 26 May, Michel Ney, the newly appointed general of division, took command of the forward line protecting the main French force at Zürich.

The following day, Friedrich, Baron von Hotze, arrived with close to 8,000 battle-hardened and experienced Austrian border troops, including the 12th Infantry Manfredini, a battalion of Hungarian grenadiers, and six squadrons of the Waldeck Dragoons.

[6] While Soult's Corps campaigned in central northern Italy, Masséna was besieged in Genoa by an Austrian army of 24,000 and a British naval squadron.

At Montecreto (13 May 1800), Gazan's division and the first column of Soult's main force (approximately 5,000 men), attacked a stronger Austrian position of 7,000, under command of Prince Hohenzollern.

Soult was taken prisoner, General of Brigade Joseph Perrin was killed, and the cavalry commander, Jean-Joseph Gauthier, was badly wounded.

The defeat could be seen from the ramparts at Genoa and caused the French garrison's morale to plummet; many units were already near mutiny and food was scarce.

[2] In the War of the Third Coalition, Gazan initially was assigned as a division commander of Napoleon's Grande Armée in Lille, in preparation for the planned invasion of England; he remained there until the idea was abandoned.

[11][12] As recognition of his conduct in "the immortal Battle of Dürenstein",[1] he received the Officers Grand Cross of the Legion of Honor and the survivors of his division was sent to Vienna to recuperate.

When Austria sued for peace, Gazan's division was sent to Würzburg in Bavaria, where it remained until Prussia declared war in October 1806.

In Fary 1811 he crossed the Sierra Morena to guard the supply On 15–21 March, his 2nd Division of the V. Corps besieged and captured the small fortified town of Campo Maior, in eastern Portugal.

The fire-fight wrought massive casualties, and the bodies were reportedly stacked three and four men high; the distinction was in 360 French muskets in deep and narrow columns versus 2000 British flintlocks in a double line of infantry.

[17] Only a costly mistake by the British commander, Major General Colborne, prevented a worse disaster for the French.

Colborne had deployed his infantry in the standard line, two men deep, and had prepared to fire close range volleys into the French flank.

Recognizing the opportunity, Latour-Marbourg's 2nd Hussars and First Vistula Lancers (a Polish unit) to attack the British line before the infantry could form its defensive squares.

The 3rd (East Kent) Regiment of Foot ("The Buffs") lost 643 of its 754 men at Albuera, most of them in the initial onslaught of French cavalry.

Despite the mounted assault, however, the French 2nd Division suffered high casualties and lost five colors, a significant blow to its morale and pride.

On 21 June, Generals Rowland Hill and Pablo Morillo moved toward the south end of the valley; Gazan and d'Erlon asked Jean-Baptiste Jourdan for reinforcements, but the Corps' commander was preoccupied with the possibility of an attack at the opposite flank, and sent none.

[20] The Allies captured the entire supply convoy, all the baggage and took many prisoners, including Gazan's wife and children,[21] although they later managed to rejoin him.

Gazan mentioned that general officers and subordinates alike "were reduced to the clothes on their backs and most of them were barefoot,"[22] but the rank and file of the army also suffered enormously from hunger, exposure, and disease.

[23] After the war, Jean-Baptiste Jourdan persuaded Gazan to be part of the Conseil convened on 9 November 1815 to try Michel Ney for treason.

Despite his oath of allegiance to the restored monarchy, the loyal Ney had rallied to Napoleon's banner immediately upon his landing in southern France and had led a corps into battle at Waterloo.

Although the King's government may have expected the Conseil to find Ney guilty, the members voted 5–2 to declare themselves incapable of reaching a verdict, and deferred the case to the Chamber of Peers.

[24] After the 1830 revolution, the new King of the French Louis Philippe made Gazan a peer of France, and he received a command of a military division in Marseille.