Vallum is either the whole or a portion of the fortifications of a Roman camp. The vallum usually comprised an earthen or turf rampart (Agger) with a wooden palisade on top, with a deep outer ditch (fossa). The name is derived from vallus (a stake), and properly means the palisade which ran along the outer edge of the top of the agger, but is usually used to refer to the whole fortification. Characteristics The stake-like valli (χάρακες) of which the vallum palisade was composed are described by Polybius (xviii.18.1, Excerpt. Antiq. xvii.14) and Livy (Liv. xxxiii.5), who make a comparison between the vallum of the Greeks and that of the Romans, very much to the advantage of the latter. Both used for valli young trees or arms of larger trees, with the side branches on them; but the valli of the Greeks were much larger and had more branches than those of the Romans, which had either two or three, or at the most four branches, and these generally on the same side. The Greeks placed their valli in the agger at considerable intervals, the spaces between them being filled up by the branches; the Romans fixed theirs close together, and made the branches interlace, and sharpened their points carefully. Hence the Greek vallus could easily be taken hold of by its large branches and pulled from its place, and when it was removed a large opening was left in the vallum. The Roman vallus, on the contrary, presented no convenient handle, required very great force to pull it down, and even if removed left a very small opening. The Greek valli were cut on the spot; the Romans prepared theirs beforehand.(Polyb. l.c.; Virg. Georg. iii.346, 347; Cic. Tusc. ii.16). They were made of any strong wood, but oak was preferred. While on the march, each soldier carried three or four strong wooden stakes each at least 1.5 m (5 ft) long and pointed at both ends. A number of these have been found in excavations, sufficiently well-preserved to show that they were "waisted", that is narrowed at the centre. It is clear that these could not have been used on their own to form the palisade of the vallum constructed around a temporary marching camp; they would have had gaps between wide enough for an attacker to pass through with ease. One suggestion is that the "waist" facilitated them