As the Middle Ages drew to a close, the French cavalry were considered among the finest - if not THE finest - in Western Europe.  Cavalry, equated with knighthood, was a gentleman's activity, one requiring exemplary courage and combat skills - plus the resources to afford the horse(s), the assistant(s), the armor, and the time to hone those combat skills.  A favored tactic was "en Haie," the all-out charge of two extended lines with lances.  The results could be splendid victories against peasants and tradesmen recruited for a campaign as foot "soldiers" (as was so often done in the Middle Ages).  Before you raise your hand to mention "Agincourt," recall that the French knights were on foot for that battle and funneled themselves into a very compromising position; consider also a battle such as Formigny, 1450, in which the English prevailed so far as to capture two French artillery pieces, then were set upon by French cavalry sweeping down in their traditional hard charge onto their flanks - the English lost 3,000 men and the battle.

But technology caught up with the gallant French knights.  At the 1525 Battle of Pavia Spanish infantry shooting those new-fangled muskets dropped many, even two horsemen with one shot, the costly armor not stopping musket balls. Add pike to the improved and increasingly abundant firearms.  A knight's lance could not reach as far as a pike, which when held by an organized group of disciplined soldiers, stopped cavalry charges.  One widely adopted change in cavalry methods was the caracole.

Henri IV, King of France, needed to make his meager force the most efficient in the French Civil/Religious Wars of the 16th Century.  Although impressed with the charging effectiveness of the cavalry of old, he reformed that arm to bring it out of the Middle Ages.  Henri IV did away with the two long lines for the attack in favor of a tighter, deeper formation, the squadron - and with that, he did away with the lance in favor of the pistol and the sword.  The galloping charge remained - it offered speed and shock.  The squadron comprised of several hundred horsemen in four or more ranks not only broke the fragile en Haie but proved flexible for other situations. The Army of Flanders, commanded by the Duke of Parma and ordered by Phillip II to interfere in the affairs of France, discovered how flexible, quick and aggressive were those squadrons. To the Spanish trudging into the French countryside at the pace of draft animals and infantry, the French mounted squadrons seemed to fly from one place to another, going to where and when they had the advantage, and hitting at those moments most inconvenient to the Spanish, like during a march.  The reconceptualized French cavalry skillfully conducted a war of attrition.

Arquebusier-á-Cheval  Note lack of bandolier and the arquebus carried by means of a sling.  Note also the soldier wears no boots nor any armor except for the infantryman's helmet. His horse is light and smaller than the cavalryman's mount.

Whilst Henri IV still had use for the mounted gentlemen of old, the gendarmerie, he knew he needed more cavalrymen than he could bring gendarmerie to his banner.  There were simply not that many of them and their bravery came at a cost: many had perished on the field of honor.  Henri IV added to their reorganized ranks the chevaux-légers, a.k.a., light cavalry whose numbers included men from outside the nobility, and what was a development in the concepts of mounted fighters, the arquebusier-á-cheval, sometimes called carabins, and elsewhere later termed dragoons: mounted infantry.

Henri IV armed his mounted infantry with arquebuses (hence the name, arquebusier-á-cheval) and the intent was for those men to provide firearm support for their mounted brethren, at a range longer than what those others had with their pistols.  He mixed units of  arquebusier-á-cheval with his cavalry squadrons and on campaign they rode together.  These mounted infantry were immediately available for any situation needing ready infantry support. At the discretion of the commander in a fight, the arquebusier-á-cheval dismounted and fired on foot as infantry (rather than in a caracole) - or they remained in the saddle. Their effect was to disrupt and "soften" the enemy before that enemy got close enough to engage the French cavalry.    The Swedish king's seemingly odd notion of interspersing musketeer units with his cavalry has this precedent and the effect he achieved was the same as what Henri IV achieved: long-range firearm cover for his cavalry.

When by 1621 when King Gustavus Adolphus began re-organizing his Swedish horse, Henri IV's innovations were spoken of by his half brother, 20 years older, Karl Karisson Gyllenhielm, who had served under Henri IV.  Taken prisoner of war by the Poles, Gyllenhielm was released in 1613 and returned to Sweden where by 1616 had been promoted to field marshal and in 1620 made Lord-Admiral of Sweden.