A Sevateem warrior handles a crossbow. (TV: The Face of Evil)
Crossbows were a type of weapon commonly used in the Middle Ages. They were a type of projectile weapon. Specially-designed bolts were the usual ammunition.
Irongron's men aimed crossbows at Linx when the Sontaran warrior talked to Irongron in his castle. One was also used by the Third Doctor to save Hal the Archer. (TV: The Time Warrior)
In 1215, at the behest of the Tremas Master, a guard at Fitzwilliam Castle killed Sir Geoffrey de Lacy by firing a crossbow at him. He was hit in the back while riding from the castle and died from his wounds some time later. (TV: The King's Demons)
The human colonists on Tara used crossbows that fired electric bolts. It was considered a peasant's weapon. (TV: The Androids of Tara)
The Sevateem used the crossbow as their primary ranged weapon. Leela was proficient in its use. The Fourth Doctor used a crossbow to shoot a pulley, preventing his descent into a pit of Horda. He credited William Tell with his knowledge of the weapon. (TV: The Face of Evil)
Crossbows were among the exhibits in a Time Museum. The Second Doctor used one to shoot a ray gun out of a Cyberman's hand. (COMIC: The Time Museum)
