While strong cities/forts and elaborate sieges to capture them were common throughout the ancient world, the Romans were unique among ancient armies in their extensive use of field fortifications. In campaign after campaign, enormous effort was expended to dig—a job done by the ordinary legionary. His field pack included a shovel, a "dolabra" or pickaxe, and a wicker basket for hauling dirt. Some soldiers also carried a type of turf cutter. With these, they dug trenches, built walls and palisades and constructed assault roads. The operations of Julius Caesar at Alesia are well known. The Gallic city was surrounded by massive double walls penning in defenders, and keeping out relieving attackers. A network of camps and forts were included in these works. The inner trench alone was deep, and Caesar diverted a river to fill it with water. The ground was also sown with caltrops of iron barbs at various places to discourage assault. Surprisingly for such an infantry centred battle, Caesar relied heavily on cavalry forces to counter Gallic sorties. Ironically, many of these were from Germanic tribes who had come to terms earlier.