Question: In the late middle ages, every knight or even his retainers and squires were armed with a spear or a lance. When heavy cavalry gave way to pike squares, we still see the lance still in use among the demi-lancers. Somewhere along the way though, they completely disappeared, surviving only in the Polish army and appropriately enough to be resurrected by them in the 18th century when the effectiveness of the Polish cavalry was shown. Since then, the lance stayed with cavalry until they became mechanized.

A possible culprit is the [Reiter](http://en.wikipedia.org/wiki/Reiter) employing the [caracole](http://en.wikipedia.org/wiki/Caracole) which showed tactical supremacy over the lancer in many battles such as [Coutras](http://en.wikipedia.org/wiki/Battle_of_Coutras) but that doesn't explain why they suddenly became resurgent again in the 18/19th century.

What caused the lance's short disappearance and why? If it indeed was firearms and caracolle tactics, then what made them become popular again later on?

Answer: 
The fall (and rise) of lances were tied to other developments regarding horse troops.

It was the (original) "cavalry" that used pointed weapons from the lances, dating back to the Middle Ages. By about the 17th century, there was a new type of horse soldier, [dragoons,](http://en.wikipedia.org/wiki/Dragoon) who were mounted infantry, rather than cavalry. As such, they were "musketeers" on horses, in contrast to "lancers." As time passed, tacticians "rethought" the value of hand weapons, and gave dragoons swords, which were easier to handle than lances, while (in some cases), replacing their heavy muskets with lighter ["carbines"](http://en.wikipedia.org/wiki/Carbine) for firing. Provided with inferior weapons and horses, dragoons were usually at a disadvantage against both infantry and cavalry in a "stand up" fight, but their combination of speed and firepower made them ideal for patrolling, scouting, seizing and holding key points, etc.

In the 19th century, the introduction of rifles changed the equation further, by making guns longer ranged, and through the addition of the "repeating" feature. At this point, riflemen on horses were at a disadvantage against riflemen on foot, but the cavalry did have the advantage of getting to key points faster. Using this advantage, cavalry would (mostly) fight dismounted, with one-fourth of the men holding the horses of three others. In a war in which (cavalry) general Nathan Bedford Forrest described as "getting there firstest with the mostest," the advantage of faster arrival often outweighed the disadvantage of a one-quarter reduction in manpower.

Even so, traditional cavalry (with lances) was still good for some things, like attacking artillery positions and "running down" fleeing infantrymen from broken formations. These advantages were more apparent in the plains of Eastern Europe (and in Spanish possessions), than in the more broken ground of the rest of Western Europe. So many East European armies reserved a some cavalry for such purposes, while other armies largely switched to infantry. In this regard, the (remaining) use of cavalry was kind of like the old rock-scissors-paper game.
The coming back part, is, IMHO well covered by [Tom Au](https://history.stackexchange.com/a/19155/12602). But the disappearance is due to modernisation of the armies in the 15th Century as well as the appearance of fire-weapons.

In the earlier Middle Age, the nobles were equiped with lances and mounted on horses. This lead to the tactical uses of heavy cavalries, which were, e.g., quite effective in the First Crusade. One should note that the effectiveness of heavy cavalries were only part due to the effectiveness of the lance, and part to a psychological effect. This is quite well illustrated in Braveheart (regardless the inaccuracies that the film may present). The problem was: this unit was highly effective, but costed a lot of money. Nevertheless, through centuries, that was considered the main unit of a feudal army. During the 100 years war, however, three factors came in: the armies [became more professional](http://www.deremilitari.org/REVIEWS/crecy_mohacs.htm), the [fire weapons](http://brego-weard.com/lib/newosp/European%20Medieval%20Tactics%202%201260-1500.pdf) which countered well cavalries unit (scaring the horses) and it was shown that those expensive units could be countered (slaughtered?) by much less expensive units ([Crécy](https://en.wikipedia.org/wiki/Battle_of_Cr%C3%A9cy), [Agincourt](https://en.wikipedia.org/wiki/Battle_of_Agincourt)).

Professional armies, rarely had the means for heavy cavalries (due to their cost), and nobles slowly retiring from effective battle-combats also reduced slowly their numbers. That coupled with effective means to fight against the once number one unit, lead to a (relative) disappearance of mounted lances on battle field of Western Europe.