Could the Persian Empire logistically support an army several million strong?

[Erpingham]

Disagree, because Roman camps added a 200-yard anti-missile buffer all round.  I would thus take Roman camps (marching, not permanent, as the latter add various facilities and stores) as a maximum, not a minimum.

But the figure being quoted is the density of the camp space, not including the defences. 

I think we are falling down here on not thinking of this as a working military operation.  Interestingly, we have discovered from two wildly different sources - a squatter camp and a Roman army camp - that the reasonable top end density is around 1000 people per hectare.  We also know from everything else that there are size constraints on camps, to make them work i.e. that a sea of several million people and animals at maximum density wouldn't work.  However, we have no real idea of how much dead ground we need between encampments and clusters to enable watering, mustering, stockpiling and so on.  I suspect we may be reaching a dead end here.

On fodder, I think some have developed a mental image that moving a horse powered army is like a cattle drive in the wild west.  Animals roam around the camp in big herds and basically look after themselves.  This might work for meat on the hoof but mounted units maintain their animals - they gather fodder if its available locally and they have time.  Troopers take their animals down to the watering point, they don't just drive them in big herds (a horse ridden all day has to be controlled in its drinking). 

[Dangun]

If 1 000 000 people congregate of themselves into a single area at 1000 people/ha or more, what is the great difficulty in 3,4 million people congregating into an area under the command of the Great King, an area moreover that they don't occupy for more than a few days at a time?

This has been addressed a couple of times already.

But since you asked, camps do not scale up linearly - a point made by Maurice (point 11, if memory serves).
Which is probably why we have not seen a camp of this size at any time in the last two millennia.

For example, because the maintenance of a camp involves leaving it regularly to get food, water, and achieve something outside of the camp, the costs of travel in and out limit total size.

[Justin Swanton]

Here's an interesting study on the size of Roman army camps. It goes into some detail - haven't read all of it yet nor seen if it confirms my hypothesis or blows it out the water. 

[Jim Webster]

Disagree, because Roman camps added a 200-yard anti-missile buffer all round.  I would thus take Roman camps (marching, not permanent, as the latter add various facilities and stores) as a maximum, not a minimum.

But the figure being quoted is the density of the camp space, not including the defences. 

I think we are falling down here on not thinking of this as a working military operation.  Interestingly, we have discovered from two wildly different sources - a squatter camp and a Roman army camp - that the reasonable top end density is around 1000 people per hectare.  We also know from everything else that there are size constraints on camps, to make them work i.e. that a sea of several million people and animals at maximum density wouldn't work.  However, we have no real idea of how much dead ground we need between encampments and clusters to enable watering, mustering, stockpiling and so on.  I suspect we may be reaching a dead end here.

On fodder, I think some have developed a mental image that moving a horse powered army is like a cattle drive in the wild west.  Animals roam around the camp in big herds and basically look after themselves.  This might work for meat on the hoof but mounted units maintain their animals - they gather fodder if its available locally and they have time.  Troopers take their animals down to the watering point, they don't just drive them in big herds (a horse ridden all day has to be controlled in its drinking).

the reason cavalry men had servants was often to cut the fodder, because if you just let animals graze it, they'll waste a lot by trampling on it, pissing on it and shitting on it.
Also they'll graze selectively and only take the nice stuff, so what's left no others will eat.
So fodder has to be within walking distance of the camp, because if you've got to ride to get it,it reduces the time the horse has to eat and digest it

[Erpingham]

Thanks Jim.  That confirms my reading too - that fodder would be gathered, not horses ridden out to hunt for pasture.  In this case, I think Herodotus has plenty of servants around but the time factor coupled with the availability of cuttable fodder within range would be key.  Other armies seem to have used cut fodder as supplemental to dry fodder or done without it.  Does Xenophon or any of the ancient authorities speak about horse care on campaign, which may guide us here?

[Duncan Head]

On fodder, I think some have developed a mental image that moving a horse powered army is like a cattle drive in the wild west.  Animals roam around the camp in big herds and basically look after themselves.  This might work for meat on the hoof but mounted units maintain their animals - they gather fodder if its available locally and they have time.  Troopers take their animals down to the watering point, they don't just drive them in big herds (a horse ridden all day has to be controlled in its drinking).

I'd sort of been assuming that the cattle-drive parallel was being applied only to the baggage-animals, and that everyone agreed that the cavalry horses would be more directly looked after. But perhaps I was wrong. And perhaps it wouldn't work even then 

[Erpingham]

I'd sort of been assuming that the cattle-drive parallel was being applied only to the baggage-animals, and that everyone agreed that the cavalry horses would be more directly looked after. But perhaps I was wrong. And perhaps it wouldn't work even then 

I think the cattle drive thing would work for meat on the hoof.  I don't think it makes sense for baggage animals, where you need to a continuity between baggage teams and loads.  The effect of masses of mule drivers wandering through herds of mules to find their own before loading them with their personalised pack saddles on the timing of the march is a bit alarming.

[Jim Webster]

On fodder, I think some have developed a mental image that moving a horse powered army is like a cattle drive in the wild west.  Animals roam around the camp in big herds and basically look after themselves.  This might work for meat on the hoof but mounted units maintain their animals - they gather fodder if its available locally and they have time.  Troopers take their animals down to the watering point, they don't just drive them in big herds (a horse ridden all day has to be controlled in its drinking).

I'd sort of been assuming that the cattle-drive parallel was being applied only to the baggage-animals, and that everyone agreed that the cavalry horses would be more directly looked after. But perhaps I was wrong. And perhaps it wouldn't work even then 

A cattle drive would only work for 'meat on the hoof', baggage animals are as individually managed as cavalry horses
(And the cattle drive would take a lot of careful managing)


If you had two bullocks pulling a cart (just as an example), they'd eat about 50lb per day dry grass. (Which is all you'd find in the area are the time.)
So your man 'parks' his bullocks. Picks up his sack and his sickle and walks through out 6000 hectare camp.  (assuming he only has to cross half of it, then I'll let you work out how long that takes him)
Then outside the camp he can start collecting grass, but the nearby stuff will either have been already taken, or will have been earmarked for cavalry horses etc (with cavalrymen lounging about making sure nobody nicks it whilst their servants cut it)
So he could have to walk a mile or so more to get to an area where the grass is fresh, he'll have to cut it, then carry 50lb back. So just the cutting could take an hour and he might have a second hour outside the camp just looking. Then there's the crossing of the camp as well.........
Indeed on reason for having so many camp followers is that one can cut grass whilst the other is 'parking the bullocks.' Cutting on the move wouldn't really be possible for a lot of them because most of the grass within easy reach of the road would have gone by the time most of the baggage got there

[Justin Swanton]

On fodder, I think some have developed a mental image that moving a horse powered army is like a cattle drive in the wild west.  Animals roam around the camp in big herds and basically look after themselves.  This might work for meat on the hoof but mounted units maintain their animals - they gather fodder if its available locally and they have time.  Troopers take their animals down to the watering point, they don't just drive them in big herds (a horse ridden all day has to be controlled in its drinking).

I'd sort of been assuming that the cattle-drive parallel was being applied only to the baggage-animals, and that everyone agreed that the cavalry horses would be more directly looked after. But perhaps I was wrong. And perhaps it wouldn't work even then 

Here's a link to the grazing area needed per horse - 20 to 50 horses per acre. Haven't worked out the implications for the Persian army.

[Erpingham]

There's a lot on pasture levels for horses out there but they are usually based on sustained grazing in a single field or paddock.

This may help, from The Horse

So, how much grass can be eaten per hour of grazing activity? This will vary with pasture forage quantity, quality, and palatability, and also with the amount of time horses are on pasture. However, about 1-1.4 pounds (0.5-0.6 kg) per hour (DM basis) is a reasonable range assuming quantity is not a limiting factor. This means that a horse with 24-hour access to good-quality pasture grazing 17 hours each day can consume up to 25 pounds (11.3 kg) as forage, which is plenty to satisfy his daily DM needs. A minimum of eight to 10 hours at pasture would be needed to achieve a DM intake of at least 1% of body weight. Anything less than this duration of grazing and the horse will need supplemental forage (such as hay) to satisfy his forage needs.

As Justin's quote points out, horses are as happy grazing at night, so if you could find the right levels of pasturage, you could probably provide a horse with half its needs in fresh fodder by grazing.  This doesn't help with the area question though.

Jim, who knows these things, might be able to assess the productivity of unimproved meadow on the basis of fodder cutting, as a comparison.

[Jim Webster]

There's a lot on pasture levels for horses out there but they are usually based on sustained grazing in a single field or paddock.

This may help, from The Horse

So, how much grass can be eaten per hour of grazing activity? This will vary with pasture forage quantity, quality, and palatability, and also with the amount of time horses are on pasture. However, about 1-1.4 pounds (0.5-0.6 kg) per hour (DM basis) is a reasonable range assuming quantity is not a limiting factor. This means that a horse with 24-hour access to good-quality pasture grazing 17 hours each day can consume up to 25 pounds (11.3 kg) as forage, which is plenty to satisfy his daily DM needs. A minimum of eight to 10 hours at pasture would be needed to achieve a DM intake of at least 1% of body weight. Anything less than this duration of grazing and the horse will need supplemental forage (such as hay) to satisfy his forage needs.

As Justin's quote points out, horses are as happy grazing at night, so if you could find the right levels of pasturage, you could probably provide a horse with half its needs in fresh fodder by grazing.  This doesn't help with the area question though.

Jim, who knows these things, might be able to assess the productivity of unimproved meadow on the basis of fodder cutting, as a comparison.

The problem is that, yes, you can graze horses over night, but somebody needs to stand guard over them in case somebody runs them off (other cavalry units in your own army are as likely to do it as barbarian horse thieves)
Also it's an inefficient use of fodder, they waste far more than if you just cut it. Herbivores selectively graze. They'll eat the stuff that's nice, ignoring stuff that's just as nutritious but is further down their list of preferences.
It's also an inefficient use of time. If the horses are grazing they have to be caught and brought in through your 6000 hectare camp to be harnessed and made ready. If they're in nice tidy horse lines to start off with, that is so much faster. The horse can still eat over night, but it does so in one place and just soils one area. You'll get much more fodder per acre if you cut and carry it to the animal

[Prufrock]

If it's any use, Xenophon mentions in the Anabasis that Persian horses are tethered and hobbled at night. (3.4.35)

[Justin Swanton]

If it's any use, Xenophon mentions in the Anabasis that Persian horses are tethered and hobbled at night. (3.4.35)

Definitely of use.    It's looking like food was taken to horses, not vice versa. Would the same apply to pack animals? I suppose it would. How would a regular army like Rome's feed its animals on the march?

[Jim Webster]

If it's any use, Xenophon mentions in the Anabasis that Persian horses are tethered and hobbled at night. (3.4.35)

It's the way I'd do it to be honest. It's far more efficient to have the cavalry horses (and draft animals) safe and eating under guard whilst some expendable servant goes out cutting fodder. It's a lot easier to get a cavalry unit into the saddle if you need them in a hurry if they don't have to conduct the last roundup first 

[Jim Webster]

If it's any use, Xenophon mentions in the Anabasis that Persian horses are tethered and hobbled at night. (3.4.35)

Definitely of use.    It's looking like food was taken to horses, not vice versa. Would the same apply to pack animals? I suppose it would. How would a regular army like Rome's feed its animals on the march?

A lot of armies had servants/slaves for cavalry, and one of their jobs would be cutting fodder. If it's only a small force the servants could probably cut stuff within sight of the road as the baggage advances.
The problem is the bigger the army, the more space the army takes up and the further the servants have to go for fodder.