Accurate archery with the longbow required enormous amounts of practice.  It was easier to become relatively dangerous with a crossbow, which meant that typically a crossbowman came cheaper than an efficient longbowman.  Both were regarded as the inferiors, in both social and strategic terms, of knights on horseback, their effectiveness at battles like Crecy and Agincourt notwithstanding.

Thankfully for the English, they had a history of taking their longbow practice seriously.  The longbow had its advantages and disadvantages, according to Michael Loades , a British historian of medieval weaponry.  The longbow could be fired more rapidly, by a ratio typically in the neighborhood of two arrows loosed for every one bolt from a crossbow.  The longbow tended to be more powerful than all but the strongest crossbows. And men could stand closer together, in a more tightly packed unit, when holding longbows.

The crossbow was nevertheless a deadly weapon. Once the crossbow was spanned (its string drawn back into position to be released) its user could wait for the most opportune moment without the requisite physical strength that a longbow required.  Using a crossbow generally required a less upright posture, often more suitable for the defensive cover of a castle’s battlements.

A number of devices were used to make spanning a crossbow easier.  One of the simplest was a hook suspended from a crossbowman’s belt that allowed the bowstring to be pulled into position by using the strength of the legs, the bow being fitted with a stirrup and held down by the user’s foot. 

Agecroft Hall’s collection includes a 17^th century crossbow with such a stirrup, quite typical for its time.

At the elaborate end of the spectrum was a device much like a windlass that drew back the bowstring. In the heat of battle, however, it is difficult to imagine such a device being anything but slow, although it did provide the user with more drawing power.

While the more powerful longbows and crossbows could pierce armor given a close enough range, it was left to gunpowder weapons to render armor obsolete on the battlefield  and castles increasingly vulnerable with the advent of larger, more powerful cannons.

Agecroft Hall’s 17^th century muzzle-loading musket, while not very accurate and slower to use in battle than later breech-loaders, is a fine example of the type that helped spell the doom of the armor-protected knight. You just can’t stop progress.