The crossbow has been around for centuries. In its earliest form, the crossbow was a simple weapon. The bow was placed on a stock and the bowstring was pulled back to be placed into a notch. The notch had a hole through which a rod was pushed to release the bowstring. The potential energy from the taut bowstring was then released and would force the bolt or quarrel down the length of the stock and, potentially into the target that the shooter was aiming at. Simple, right.
As crossbows became more complex, they also realized that the crossbow had certain advantages over a traditional bow. The bow most be drawn and then held by the shooter until he has picked a target and has released the bowstring. A bow with a 50-75 lbs pull can make this endeavor very tiring during prolonged combat. Traditionally, this is why archers with bows fired in mass. You fought a battle of attrition with archers not precision. With a crossbow, the tension is held by the crossbow, not the archer. this gives the crossbow wielder the ability to be more choosy about his target and wait for the right time to strike.
Once this was discovered, makers of crossbows begin to see how much weight they could put on their weapons. Pounds and pounds of force were put on the crossbows in hopes of achieving the right balance between speed in reloading and power delivered to the quarrel or bolt. The only problem that these weapon designers found was the fact that as the pull on the bowstring got heavier and heavier, the warrior using the weapon could not pull it back. At this point, straps were added to the front of smaller crossbows so that you could use your foot and some leverage to cock your weapon and on large siege defense crossbows a small crank was added to the side of the crossbow allowing even more tension to be placed on the bow. In examples of crossbows with cranks, these large, heavy crossbows would put a bolt through armor, especially chain maille.
The picture to the left is a modern crossbow bolt. You have all seen an arrow. Do you notice the difference. You still have a cylindrical piece of ammunition with a pointy end and even in ancient bolt and quarrels which had fletching on the end of the bolt or quarrel you still had a much hardier version of an arrow. Bolts don’t have the same characteristics as an arrow in flight. Arrows need lift to reach their target, due to the power that a crossbow is fired with, the ammunition does not lose height on its flight nearly as quickly. Again, accuracy and power, tat is the amazing part of a crossbow.
Crossbows lost popularity as gunpowder and guns took to the battlefield. However, the crossbow still held sway with some of the stealthier and more grisly parts of society. Assassins and others in their field of work still enjoyed the quiet attack allowed by the crossbow and the fact that a heavy crossbow could punch through armor.