Formations arriving on the battlefield
Is it the case that at the scale of ESR the exact nature of a formation in column of march is immaterial and is effectively already taken into account in the ployed formation and deployment rules?
Basically, yes, exactly what you're concluding here.
Or would it be reasonable to bring a ployed formation on to the table in several columns so that they take up less room and arrive much faster?
A Force could certainly enter the battlefield in multiple ployed columns, I suppose it innately must, but they could and sometimes should arrive by different roads or even different directions. But a ployed Formation innately can't, as doing so would effectively mean the Formation isn't ployed. Could a Formation enter the battlefield deployed? Sure.
Basically, we're not looking at tactics, we're looking at grand tactics, a 700-man battalion may have a dozen support vehicles and a couple battalions guns traveling with it. How are those traveling? No idea, hopefully in the correct configuration to accomplish what you're saying. What we know is that the 5,000-15,000 man division is currently in a march state [ployed] not a battle state [deployed]. The micro of how the march is carried out and is a given battalion ready for action or has it blocked its ammo wagons or are its battalion guns jamming the road, is below the scope of ESR. Whereas the focus is on the macro state of that battalion's division and whether it is in a fighting state or the desired position.
All of the videos of games of ESR I have seen and the illustrations in the rules show formations arriving on the battlefield strung out in one long column of march along a road. Is this really how armies marched?
Whether a corps or similar sized Force used one or multiple roads really depended on the battle and the logistical concerns, i.e. are there several useable roads that lead where we need them to? But in short: Yes, this is really how period armies marched.
If armies march in a long line down a road then a Corps could be several miles long, so it would require two or three hours at walking pace for the tail of the force to arrive and deploy. When you scale this up to an army of several Corps then the time taken would be increased accordingly. Ideally of course an army would not be marching down one road but arriving from several different directions, but for some campaigns this may not be possible, such as the French at Waterloo following the main road that led to Brussels.
The question here is which scale of element uses "one road", does a division use a single road? Yes, most commonly through the period, divisions did not generally breakup into their component brigades and all take different routes.
Does a corps use a single road? Often but not always, it really depends on the options.
Does an army use a single road? More and more we see that the armies of the period tried not to as the period progressed, but it still happens. Even as late as 1812, large portions of the French main army are using a single road simply because it was the best and sometimes only option.
Did it take 2-3 hours for a corps-sized element to arrive and deploy via one road? Yes, we see this is exactly the case, Davout at Eylau, Victor and Ney at Friedland, Eugene at Ostrovno (Vitebsk), Davout again at Schewardino, i.e. basically any time a corps is compelled to take a single route due to the available road network and competing logistics of the other corps, this is exactly what happens.
Does this scale directly? Actually, it is generally worse because there are intentional gaps between each sub-element that occur both naturally and to allow some flexibility to reduce traffic jams. But yes, if an army is compelled to take a single road, of course this gets worse. We see the wings of the Austrian army using a single route during the first phase of 1809 when Hiller is retreating. The Russian army only has a couple roads to Moscow from Borodino, and before that, had only one road the majority of the way from Smolensk to Borodino.
One of the reasons that the French are so successful in concentrating at Jena is that the different corps d'armée are marching by different parallel roads (still multiple corps per road, because again, only so many roads available) and able to arrive from different vectors.
So, yes, depending on the road network, it can take a long time. This is why many large Napoleonic battles occur the day after the opposing army arrives, it takes time for the two to jockey into the positions they want and for them each to arrive.
In reality would a force have split into several columns, with infantry and cavalry marching parallel with the road, while the road itself would have been reserved for the artillery and other wheeled transport? This would seem a practical way of bringing armies onto the battlefield as quickly as possible and would also speed up deployment. It would also be more tactically flexible than having troops strung out over several miles of road.
If what you mean is, do the infantry march in two narrow columns on each side of the road so that the road itself is clear for vehicles as is commonly depicted in film of WW2, that sort of thing is completely abstracted in ESR. An "infantry division" that might have a division commander, 12 battalions of infantry, 2 artillery batteries, and a Reformation Area may take up approximately 2 miles of our tabletop battlefield (at 1"=150 yards). That distance isn't only the infantry of those battalions, but also all their vehicles (a French infantry battalion in 1806 may have upwards of 15 supply vehicles). In ESR, all those vehicles are "in there somewhere" and simply symbolized during battle by the Reformation Area.
Hope this helps.
thank you for your prompt and comprehensive response. What you say makes sense, so I guess if I want to spend less time moving long columns of troops onto the table then I should either increase the number of roads leading onto the battlefield or increase the number of formations on the table at game start.