The March.
When the trumpet gave the signal (
signum profectionis) to break up camp (
castra movere), the soldiers struck their tents and packed their baggage (
vasa conligere); at the second signal the baggage (
impedimenta) was put on the pack-animals and in the wagons; at the third signal the army (
agmen) began its march. The start was made usually at sunrise, but it might be made earlier on special occasion. The ordinary day's march lasted about seven hours, and covered about 15 miles; a forced march (
magnum iter) about 25. Caesar made many such, his men travelling immense distances with incredible swiftness.
When marching in the enemy's country, the main body of troops (
agmen) protected itself by a vanguard (
agmen primum) of cavalry, light-armed infantry, and scouts (
exploratores), and by a rear guard (
agmen novissimum). Sometimes individual spies (
speculatores) were sent far in advance to reconnoitre the country and the movements of the enemy's forces.
The order of march of the main body depended on the nearness of the enemy. When no enemy was near, each legion marched in a single column and was followed by its baggage train (see
Bk. ii. 17). In the neighborhood of the enemy, a single column of troops in fighting trim (
expediti), i.e. without packs (
sarcinae), followed directly after the vanguard; then came the baggage of the whole army, while the remaining forces acted as a rear guard (cf. Bk.
ii. 19). Sometimes, for additional security against flank attacks, columns of infantry marched on each side of the baggage train, forming a hollow square (
agmen quadratum; see Fig.
73). If, when marching in this order, the army was compelled to halt and defend itself, the soldiers, by facing about, presented to the foe a complete circle (
orbis) of armed men. When the foe was near and the ground level and open, the march was sometimes made in three parallel columns, which, by a simple evolution, could be quickly changed to the triple battle line (
acies triplex), the regular formation for an engagement.
Streams were crossed either by fords or bridges. Romans could cross deeper fords than we, for they had no powder to keep dry (cf.
Bk. v. 18). Sometimes a line of cavalry was sent across the stream to break the force of the current (cf.
Bk. vii. 56). Bridges were usually very simple affairs of logs covered with earth and brush, or of boats, but Caesar's masterpiece of military engineering was his roadway forty feet wide with which he twice spanned the Rhine (
Bk. iv. 17;
Bk. vi. 9; see Figs.
59,
80).
