Battle at the pontes longi

Annex C: Battle at the pontes longi

The Roman writer Tacitus reports that the Roman army after the battle in the rough (s. App. B) in 15 AD immediately withdrew from Germania. This suggests that the Romans suffered very heavy losses; especially their cavalry and auxiliary troops appear to have been significantly stricken.

Germanicus, who was at that time west of the Weser, initially withdrew to the Ems and then led 4 legions on the river and sea back to the Lower Rhine.
These suffered heavy losses by a storm surge. Previously, he ordered the general Caecina, with four legions, namely, the 1st, 5th, 20th and 21st (all in all, 28 000 to 30 000 men, including baggage train), to repair a path called "pontes longi" ("long bridges") that was built by the Romans around the year 1 AD: "Caecina, who led his own force, was returning by a well-known route, but was none the less warned to cross the Long Bridges as rapidly as possible." Since wood boardwalks were unsuited for the movement of Roman legions, the pontes longi must have been causeways.

When Caecina and his troops reached the causeway which was in a desolate state, they were surrounded by Arminius' warriors who had been marched up in much greater numbers than expected,
in such a way that the Romans repaired the causeway in the swampy valley, while the Germani camped on the wooded height. So Caecina led build a camp, while the other part of the troops were busy with the attacks of the Germani. After heavy and lossy fighting the Romans retreated in the evening back to camp. The Germani then let flow down water masses from the heights by diverting creeks, which also foiled the aboriously built causeway. The next day the Romans gave up the further construction on the causeway and continued their march via a elevated plane which however apparently was too narrow to allow for the planned "square formation", by which the baggage in the middle should be protected by the 5th and 21st legion which were set on the flanks,  whereas the 20th formed the rearguard and the 1st the vanguard. However the legions on the flanks abandoned their position and gave the Germani the opportunity to attack the baggage. In the battle for the baggage mainly the 1st Legion distinguished itself by courageously fighting against the Germani. Soon the way led again in swampy terrain; in the evening the Romans were finally able to fight their way under enormous losses to a dry terrain, where they built a makeshift camp and hardly had some supply.

Wikipedia: Die Schlacht an den Pontes longi

Thus the starting point for the events of the Battle of the Pontes longi is the location of the Battle on the wilds, the Plackwad south of Warstein. From here or rather from the north adjacent Haar Caecina led the 1st, 5th, 20th and 21st legion to the Rhine. However e could not take the shortest route, which would have led him to Vetera/Xanten, but he had to make a detour to repair the pontes longi. Thus the pontes longi probably were the causeways through the Wuppertal Depression (s. chap. 2.4.1), in order to cross the Rhine at Novaesium/Neuss.
At the march through the Wuppertal Depression, at first the Germani were able to attack the Romans from the wooded heights in the valley of the Ennepe between Hagen and Gevelsberg.

Schlacht an den Pontes longi Tag1
Fig. C-1: Battle at the pontes longi day 1, march of the Caecina legions (blue) and the baggage (dark blue) through the Ennepe valley, attack of the Germani (red)

On the ridge of the Linderhauser Ruecken on the 2nd day of the battle the Romans were able to march in a rudimentary square formation, in order to reach at Heckinghausen the valley of the Wupper and thus to move back in swampy terrain.

Battle at the Pontes longi day 2
Fig. C-2: Battle at the pontes longi day 2, march of the Caecina legions (blue) and the baggage (dark blue) in square formation via the Linderhauser Ruecken, attack of the Germani (red)

In Sonnborn the Romans were able to leave the Wuppertal Depression and at this thime they had fought their way to dry terrain.