I’m omitting a few words in this sentence to focus on the part in question. Aurigae … ita currus conlocant ut, si illi a multitudine hostium premantur, expeditum ad quos receptum habeant. The charioteers … place together the chariots in such a way that, if those should be pressed by a multitude of the enemy, they would have an unimpeded retreat. I have a book published by a Latin professor that calls the ut clause a result clause. But doesn’t the deliberate placement of the chariots indicate the purpose of providing a ready retreat?