This task is about writing a correct answer for the reading comprehension task. Based on the information provided in a given passage, you should identify the shortest continuous text span from the passage that serves as an answer to the given question. Avoid answers that are incorrect or provides incomplete justification for the question.
Q: Passage: In military affairs, the use of infantry with specialised roles increased. Along with the still-dominant heavy cavalry, armies often included mounted and infantry crossbowmen, as well as sappers and engineers. Crossbows, which had been known in Late Antiquity, increased in use partly because of the increase in siege warfare in the 10th and 11th centuries.[AB] The increasing use of crossbows during the 12th and 13th centuries led to the use of closed-face helmets, heavy body armour, as well as horse armour. Gunpowder was known in Europe by the mid-13th century with a recorded use in European warfare by the English against the Scots in 1304, although it was merely used as an explosive and not as a weapon. Cannon were being used for sieges in the 1320s, and hand-held guns were in use by the 1360s. Question: What led to the increased use of armor in the 12th century?
A:
The increasing use of crossbows