March speed rates

[Renatus]

Some average daily rates of march can be calculated from Ammianus Marcellinus' account of Julian's Persian campaign. This is for an army on campaign with baggage but with its heavy equipment (siege engines, etc.) and provisions carried by water transport on the Euphrates. The army was marching in agmen quadrata through hostile territory but largely unopposed, mostly in the month of April. Distances and speeds are given following the course of the river and, in brackets, cutting out its meanders.

Cercusium to Dura Europos - 32 miles - 2 days - 16 miles per day
Dura Europos to Anatha - 106 miles (85 miles) - 4 days - 26.5 miles (21.75 miles) per day
Deserted fort to Baraxmalcha - 23 miles - 2 days - 11.5 miles per day

Ammianus describes the stretch between Dura Europos and Anatha as an easy march (itinere levi)(Amm.24.1.6). We do not know whether the daily averages for the other stretches are lower because the going was harder or because the destination was reached earlier on the last day.

I would like to add to this post. The lower daily average for the Cercusium to Dura Europos stretch is probably due to a late start on the first day. Ammianus implies that the march was undertaken in two stages: Cercusium to Zaitha on Day 1 and Zaitha to Dura Europos on Day 2. The distances are Cercusium to Zaitha 7 miles and Zaitha to Dura Europos 25 miles. The reason for the delay is that, having crossed the river Abora on a bridge of boats and the bridge having been then destroyed, Julian reviewed and addressed the army before setting off. All this would have taken a substantial part of the first day, leaving time for only the relatively short march to Zaitha that day. The remainder of the distance to Dura Europos was covered the next day at a rate somewhat similar to the average for the next stretch.