Detailed Instructions: In this task, you are given a question and a context passage. You have to answer the question based on the given passage.
Q: What fact makes the idea of the movement possible?, Context: During the Second Punic War in 218 BC, the Carthaginian general Hannibal probably crossed the Alps with an army numbering 38,000 infantry, 8,000 cavalry, and 37 war elephants. This was one of the most celebrated achievements of any military force in ancient warfare, although no evidence exists of the actual crossing or the place of crossing. The Romans, however, had built roads along the mountain passes, which continued to be used through the medieval period to cross the mountains and Roman road markers can still be found on the mountain passes.
A:
The Romans, however, had built roads along the mountain passes