Cuirassiers were mounted cavalry soldiers equipped with armour and firearms, first appearing in late 15th-century Europe. They were the successors of the medieval armoured knights. The term is derived from cuirass, the breastplate armour which they wore.
The first cuirassiers did not appear very different from the medieval knights; they wore three-quarters armor that covered the entire upper body as well as the front half of the legs down to the knee, and the only items of equipment which differentiated them from knights were leather riding boots (as opposed to armoured sollerets/sabatons) and the use of wheel-lock pistols, in addition to lances and swords.
The armor worn by cuirassier regiments gradually decreased as time went by until by the time of the Napoleonic wars it was limited to a helmet and in some armies; such as those of France, Austria, Prussia and Russia; breastplates. There has been debate over the value of this survival since a breastplate does not provide significant protection against musket fire. It would however have had some psychological effect (effectively making the cuirassier more willing to plunge into the thick of fighting) and would have added weight to a charge, especially in cavalry against cavalry actions.
The first recorded cuirassiers were formed as 100-strong regiments of Austrian kyrissers recruited from Croatia in 1484 to serve the future Holy Roman Emperor Maximilian. They fought the Swedes and their allies in 1632 in Lützen and killed the Swedish king Gustavus Adolphus. The French introduced their own cuirassiers in 1666. By 1705, the Holy Roman Emperor's personal forces in Austria included twenty cuirassier regiments. Imperial Russia formed its own cuirassier regiments in 1732, including a Leib Guards regiment. The Russian cuirassier units took part in the Russo-Turkish War.
Cuirassiers played a prominent role in the armies of Austria, Frederick the Great of Prussia and of Napoleon I of France. The latter increased the number of French cuirassier regiments to fourteen by the end of his reign. The actual utility of this armour is questionable. Prussian cuirassiers abandoned the cuirass before the Napoleonic Wars as did the British. The Austrian cuirassiers wore only the breastplate and helmet. Napoleon, however, thought it sufficiently useful that he had cuirassier-style armour issued to his two carabinier regiments as well after the battle of Wagram. It was perhaps the psychological effect of the armoured cavalry on the battlefield that made the cuirassier such an effective component of an army.
Cuirassiers were generally the senior branch of the mounted arm, retaining their status as heavy cavalry—"big men on big horses". While their value as a heavy striking force in Napoleon's campaigns ensured the continued use of a number of cuirassier regiments in the French and Prussian armies during the nineteenth century, the expense and inflexibility of this arm limited their existence in other countries to Guard units.
In 1914 there were still cuirassiers in the German army (ten regiments including the Gardes du Corps and the Garde-Kürassiers); the French (twelve regiments) and the Russian (three regiments, all of the Imperial Guard). The German and Russian cuirassiers had, by the end of the nineteenth century, come to retain their breastplates only as part of their peacetime parade dress, but the French regiments wore the cuirass (with a cloth cover) and plumed helmet on active service during the first weeks of World War I. The three Household Cavalry regiments of the British Army (1st and 2nd Life Guards and Royal Horse Guards) had adopted cuirasses after the Napoleonic Wars as part of their full dress, but never had occasion to wear this armour in battle.
The retention of this magnificent but obsolete armour for active service by the French Army in 1914 appears to have reflected the prestige of this branch of the cavalry, dating back through the Franco-Prussian War to the campaigns of Napoleon. Attempts were made prior to the outbreak of war to have the cuirass restricted to parade dress, but on mobilisation, the only concession made was to wear a cover of brown or blue cloth over the steel and brass of the cuirass itself, to make the wearer less visible. The cuirass ceased to be worn by most French regiments within a few weeks of the outbreak of war, though it was not formally withdrawn until October 1915.
The Russian and German cuirassiers ceased to exist with the overthrow of the Imperial regimes in both countries (February 1917 and November 1918 respectively). The French cuirassiers continued in existence after World War I but with their numbers reduced to the six regiments which had been most decorated during the war. Ironically five of these had achieved their distinctions serving as "cuirassiers à pied" or dismounted cavalry in the trenches. The surviving cuirassier regiments were amongst the first mounted cavalry in the French Army to be mechanised during the 1930s. Two cuirassier regiments still form part of the French Army - the 1er-11e Régiment de Cuirassiers based at Carpiagne and the 6e-12e Régiment de Cuirassiers based at Olivet.
A few present-day mounted cavalry units continue to use cuirasses as part of their parade equipment on formal occasions. Most however have not retained the actual title of "cuirassiers", if indeed they bore it in the first place. These are the Life Guards and Blues and Royals of the British Household Cavalry; the Coraceros de la Guardia Real of the Spanish Royal Guard (created in 1875); and the Italian Corazzieri, the honour guard of the President of the Italian Republic.
In the Beyond the Sword expansion pack for the turn-based strategy game Civilization IV, they appear as a mounted unit intermediate in power and time between Knights, in the Medieval pattern, and Cavalry, who carry carbines in the game.