The lance was the primary shock weapon of medieval heavy cavalry, used from horseback to deliver reach, momentum, and formation pressure.
The lance is the cavalry spear of the high and later Middle Ages, used couched — locked under the arm against the body — so that the weapon delivers the full momentum of horse and rider at a single point.
That technique is the whole story. A spear thrown or thrust delivers the strength of a man's arm; a couched lance delivers the mass of a charging horse, and the difference is a change of kind rather than of degree.
It became the defining weapon of the mounted warrior class and the basis of the shock charge that dominated European battlefields for roughly four centuries.
A war lance runs typically 3 to 4 metres and weighs 2 to 4 kilograms, most often of ash. It is far heavier and thicker than an infantry spear because it must survive an impact that would shatter a lighter shaft.
The mature form is not a plain pole. From the fourteenth century the shaft swells behind the grip and narrows again, so the hand sits in a waisted section that resists the weapon being driven backward through the grip on impact.
Two fittings complete the system. The vamplate, a conical steel guard, protects the hand, and the lance rest — a bracket bolted to the right side of the breastplate — takes the shock into the armour and the rider's body rather than into his arm alone.
The couched charge works by mass and cohesion. Riders advance knee to knee at a controlled pace and strike together, and the effect depends far more on the formation arriving intact than on any individual's skill.
It is a single-use weapon in practice. Lances shatter on impact or are abandoned in a target, which is why every man-at-arms carried a sword, a mace or a hammer for the fight that followed — the lance opens the engagement and rarely survives it.
It could be stopped, and increasingly was. At the Battle of Bannockburn in 1314 English cavalry broke on Scottish schiltrons of spearmen, and the Battle of Agincourt in 1415 saw the French dismount most of their men-at-arms precisely because a mounted charge into prepared positions had become a poor bet.
Its strength is unmatched shock. Nothing else in medieval warfare concentrates that much energy on that small an area, and a well-delivered charge against unsteady infantry or disordered cavalry decides a battle in a minute.
Its weaknesses are ground, cohesion and the enemy's preparation. Mud, slopes, ditches, stakes and hedges all break a charge, and a charge that arrives ragged achieves nothing while presenting the horses to be killed.
It is also nearly useless afterwards. Long, unwieldy and probably broken, the lance is discarded as soon as contact is made, so its user needs a full secondary armoury to remain in the fight.
The couching technique spreads in the eleventh and twelfth centuries, and the Bayeux Tapestry catches the transition: it shows Norman riders at the Battle of Hastings in 1066 holding spears overhand, underhand and couched, all at once.
The thirteenth century is its unchallenged period, and the Battle of Bouvines in 1214 is the classic demonstration of massed heavy cavalry deciding a major engagement.
From the fourteenth century infantry answers accumulate — pike blocks, archery, dismounted men-at-arms, field fortification — and the lance stops being decisive on its own, though it remains standard cavalry equipment into the sixteenth century and survives longest in the tournament.
French and Burgundian practice represents the mature Western form: heavy lance, vamplate, lance rest, and the whole harness engineered around delivering and absorbing the charge.
Iberian warfare kept lighter cavalry and lighter lances alongside the heavy tradition, since the frontier campaigning of the peninsula rewarded speed, raiding and pursuit more than a single decisive shock.
Eastern and Central European practice developed its own heavy lance traditions, and Polish and Hungarian cavalry carried the couched lance forward into the early modern period after Western Europe had largely moved on.