| Recognizing the Timber Wall and Ditch, predating the more familiar Hadrian’s Wall, highlighted central importance of timber engineering to the Roman army in the field and took this research in an unexpected direction.|
While many Roman military installations are identified by their bank and ditch, as archaeological remains they are often somewhat underwhelming, certainly compared with some hill forts, but history attests to their success in withstanding assault.
From the outset of Caesar's account of the Gallic War, ditches and timber ramparts are a key component of the campaigns in this case used to block the migration of the Helvetii;
The tactics behind these structures can be explored by using a simple SketchUp model of the sort of rampart and ditch described by Caesar
, which can help illustrate how could a 12' high pile of wood with a ditch in front could stop whole armies.
Meanwhile, with the legion which he had with him and the soldiers which had assembled from the Province, he carries along for nineteen miles a wall, to the height of sixteen feet, and a trench, from the Lake of Geneva, which flows into the river Rhone, to Mount Jura, .……
C. Julius Caesar. Caesar's Gallic War; 1.8 In our contemporary visual culture for this period there is a tendency to see these structures as a bank of earth with a vertical timber palisade at the top. Reconstructions, such as those at the Lunt and Vindolanda follow this pattern., .
He orders him to fortify a camp with a rampart twelve feet in height, and a trench eighteen feet in breadth. …
is based on typical proportions given by Caesar, and is painted to look like sort of timber wall with horizontal timbers interlocked between a grid of posts, evidenced on the berm of Hadrian’s Wall.
Selection C. Julius Caesar. Caesar's Gallic War; 1.6Caesar, on learning these proceedings from the deserters and captives, adopted the following system of fortification; he dug a trench twenty feet deep, with perpendicular sides, in such a manner that the base of this trench should extend so far as the edges were apart at the top. He raised all his other works at a distance of four hundred feet from that ditch; …………..
……..Having left this interval, he drew two trenches fifteen feet broad, and of the same depth; the innermost of them, being in low and level ground, he filled with water conveyed from the river. Behind these he raised a rampart and wall twelve feet high; to this he added a parapet and battlements, with large stakes cut like stags' horns, projecting from the junction of the parapet and battlements, to prevent the enemy from scaling it, and surrounded the entire work with turrets, which were eighty feet distant from one another.
Selection C. Julius Caesar. Caesar's Gallic War; 7.72
The model is populated by “Sarah” from the SketchUp Team, who serves as a human scale for both attackers and defenders, and is sufficiently anachronistic to remind the viewer this is a diagrammatic scale model. There is no particular attempt reproduce the structure or the weapons in any particular detail, and again these are for illustrative purposes only.
The model has simple two story towers; these give the defenders better range and additional angles for crossfire. The ditch has a counterscarp bank, which is evident on Hadrian’s Wall, and while this might be perceived as offering slight advantage to the attacker, it also makes the ditch more difficult to escape from – assuming you had the misfortune to end up there.Killing at range
This is type of engagement is very different from the ‘meat grinder’ pitch battle with the close formations of heavy infantry we associate with the Roman army; if faced by superior numbers or position, it was much easier to fight from on top and behind a stack wood similar in scale to double-decker bus
The dimensions given by Caesar are unlikely to be arbitrary, and the model assumes they reflect the effective range of Roman weapons. While it possible for specialist to throw or shoot a projective over long distances, what matters in this context is accuracy, power, and the ability to deliver a volley of to maximise the impact; cutting down a group of attackers simultaneous is far more effective in breaking up a charge than picking off individuals.
While it is possible to use slings and even bows at this range, the significance of setting an outer perimeter 400’ probably reflects the effective range of artillery set in turrets and towers.
The view from a 24' tower of a target at 400' / reverse view above left.
Projectile weapons with a head represent a piece of iron that had to be carried to the battlefield, and which, once discharged, was effectively lost; in this respects, stones and other similar projectiles fired by slings or even artillery had an advantage, and thus were ubiquitous on ancient battlefields.
Slings and bows offer alternative trajectories as both can be delivered from high angles and from behind cover. The defenders can have a hoarding, roof, gallery or second fighting platform, to protect them from hail of missiles. Arrows and stones are small arms, a good shield and body armour should protect against the worst – or there is little point of carrying the extra weight. However, protection and tactics developed in a world of arrows and slingshot were usually ineffective against a high velocity artillery dart.
Roman artillery was a key technological advantage over their enemies in Western Europe, and was routinely used by the legions in the field, principally taking the form of large torsion powered crossbows, [left Trajan's Column]
, [sometimes also called ballistas
]. These fired large bolts, typically a pyramidal iron point, with power and accuracy engaging the enemy directly at this unprecedented range. In addition, it has been suggested that they could fire 4 rounds a minute, allowing the weapon to be retargeted on the same formation as they closed on the rampart and came in range of the principle weapon the pilum
Whites of their eyes.
The principle weapon in this type of fighting would be the spear, javelin, or more specifically the Pilum; unlike a bow, it can be used with one hand, and from behind a shield.
The view from a 24' tower of attackers at a range of 80' and closer.The Roman pilum was typical of Roman no-nonsense military hardware, with a relatively small hardened pyramidal iron head on long shank, with a heavy wooden shaft, designed to focus all the force to punch through shields and armour. [Sarah’s pila are quite short]
At about 80’ the defenders could launch the first volley of pila with the considerable advantage of 12’ or more of additional height. At this range, even if it did not kill, the hardened point of pilum range could piece shields, and then softer shank would bend rendering the weapon and the shield useless [below right]. This effect is described in a battle by Caesar.
His soldiers hurling their javelins from the higher ground, easily broke the enemy's phalanx. That being dispersed, they made a charge on them with drawn swords. It was a great hindrance to the Gauls in fighting, that, when several of their bucklers had been by one stroke of the (Roman) javelins pierced through and pinned fast together, as the point of the iron had bent itself, they could neither pluck it out, nor, with their left hand entangled, fight with sufficient ease; so that many, after having long tossed their arm about, chose rather to cast away the buckler from their hand, and to fight with their person unprotected.
Selection C. Julius Caesar. Caesar's Gallic War; 1.25
The attackers have to carry a shield and a weapon, and this leaves their right hand side unshielded, especially when throwing a missile, so the defenders will concentrate fire from their left onto the attacker right side.
The view from the rampart of attackers at a range of 80' and closer.
Realistically, they have close on the defences as quickly as possible, in close formation, suitably shielded, while carrying the weapons and equipment needed to cross the ditch and assault the rampart, while simultaneously, keeping up a hail of covering fire.
I don’t want to discuss Alisia
in detail, but this extraordinary battle does revolve around the defence of this type of structure; this was a hill fort where Vercingetorix
was besieged by Julius Caesar’s Forces, who had built a double ring of fortifications to keep the Gauls in and the relieving forces out.
The final battle eventually turns on the Gaul’s attempt overwhelm the Roman defences at the only point where the topography gave them a height advantage. 85.…. The least elevation of ground, added to a declivity, exercises a momentous influence. Some are casting missiles, others, forming a testudo, advance to the attack; fresh men by turns relieve the wearied. The earth, heaped up by all against the fortifications, gives the means of ascent to the Gauls, and covers those works which the Romans had concealed in the ground. Our men have no longer arms or strength.
86….. Caesar, on observing these movements, sends Labienus with six cohorts to relieve his distressed soldiers: he orders him, if he should be unable to withstand them, to draw off the cohorts and make a sally; but not to do this except through necessity. ………: hither they bring the engines which they had prepared; by the immense number of their missiles they dislodge the defenders from the turrets: they fill the ditches with clay and hurdles, then clear the way; they tear down the rampart and breast-work with hooks.
87.……… orders part of the cavalry to follow him, and part to make the circuit of the external fortifications and attack the enemy in the rear. Labienus, when neither the ramparts or ditches could check the onset of the enemy, informs Caesar by messengers of what he intended to do. Caesar hastens to share in the action.
88.…….. Our troops, laying aside their javelins, carry on the engagement with their swords. The cavalry is suddenly seen in the rear of the Gauls; the other cohorts advance rapidly; the enemy turn their backs; the cavalry intercept them in their flight, and a great slaughter ensues. ……
Selection C. Julius Caesar. Caesar's Gallic War; 7.85 - 7.88 What is significant in this account, it is only when the defences are being overwhelmed that the defenders have to resort to using their swords; in hand to hand fighting, superior numbers and unfavourable ground would start to tell. In the eventuality, and quite typically, the Romans counter-attacked, and the Gauls broke up and fled, for fear being trapped against the fortifications.
Above left; An attacker in the ditch as viewed from a 24' tower.
This tactic of counter-attacking was not necessarily the last resort, ramparts offer concealment, in the sense that may be difficult for the attacker to perceive the dissolution of forces, and from that, their intent. Building a rampart my look like a defensive posture, but may in fact be an elaborate ruse to get the enemy into a position where they can be caught in just such a counter attack. 
Assaulting such a structure head-on would be very dangerous, but if you failed, turning your back on it was probably worse, although preferable to being driven too close rampart or even into the ditch and being trapped in the killing zone by the press of men behind you.
References and further reading
 C. Julius Caesar. Caesar's Gallic War. Translator. W. A. McDevitte. Translator. W. S. Bohn. 1st Edition. New York. Harper & Brothers. 1869. Harper's New Classical Library.
 Birley, R. 2009 Vindolanda: A Roman Frontier Fort on Hadrian’s Wall. Amberley; Plate 1; Turf Wall reconstruction.
 see; C. Julius Caesar. Caesar's Gallic War. ch.5.51-5.53.