Before 1900, armies usually lost more men from infectious disease than combat, particularly in extended campaigns. At least that seems to have been the case in modern Western history.
There are indications that infectious disease was qualitatively different – less important – in the Roman legions. For one thing, camps were placed near good supplies of fresh water. The legions had good camp sanitation, at least by the time of the Principate. They used latrines flushed with running water in permanent camps and deep slit trenches with wooden covers and removable buckets in the field. Using those latrines would have protected soldiers from diseases like typhoid and dysentery, major killers in recent armies. Romans armies were mobile, often shifting their camps. They seldom quartered their soldiers in urban areas – they feared that city luxuries would corrupt their men, but this habit helped them avoid infectious agents, regardless of their reasons.
They managed to avoid a lot of serious illnesses because the causative organisms simply weren’t there yet. Smallpox, and maybe measles, didn’t show up until the middle Empire. Falciparum malaria was around, but hadn’t reached Rome itself, during the Republic. It definitely had by the time of the Empire. Bubonic plague doesn’t seem to have caused trouble before Justinian. Syphilis for sure, and typhus probably, originated in the Americas, while cholera didn’t arrive until after 1800.
West Hunter 
So, the causative organisms weren’t there yet because…. they evolved later, or they were there in the soil but needed hosts to transport them, and population density did the trick for them (people and their horses and cattle) by the Middle Ages?
Or they came from somewhere else.
Maybe some diseases hadn’t yet come on the scene, but there were others that had already wiped out whole armies, and the precautions the Romans took are evidence that they knew about such risks.
Here, for your enjoyment, is Byron’s Destruction of Sennacherib (loosely based on 2 Kings 19:35). Apparently this disease caused respiratory distress in horses, and in humans sudden cardiac arrest. Worth digging a few latrines to avoid.
The Assyrian came down like the wolf on the fold,
And his cohorts were gleaming in purple and gold;
And the sheen of their spears was like stars on the sea,
When the blue wave rolls nightly on deep Galilee.
Like the leaves of the forest when Summer is green,
That host with their banners at sunset were seen:
Like the leaves of the forest when Autumn hath blown,
That host on the morrow lay withered and strown.
For the Angel of Death spread his wings on the blast,
And breathed in the face of the foe as he passed;
And the eyes of the sleepers waxed deadly and chill,
And their hearts but once heaved, and for ever grew still!
And there lay the steed with his nostril all wide,
But through it there rolled not the breath of his pride;
And the foam of his gasping lay white on the turf,
And cold as the spray of the rock-beating surf.
And there lay the rider distorted and pale,
With the dew on his brow, and the rust on his mail:
And the tents were all silent, the banners alone,
The lances unlifted, the trumpet unblown.
And the widows of Ashur are loud in their wail,
And the idols are broke in the temple of Baal;
And the might of the Gentile, unsmote by the sword,
Hath melted like snow in the glance of the Lord!
Legionella pneumophila is another waterborne new disease, worthy of your attention. It found a nice niche in air conditioner systems and warm water recycling. Now that it has developed a workable survival/transmission cycle, it must be evolving like crazy and I’m afraid soon it will infect public park fountains and cascades. Another new bug is Nocardia spp., very common in wastewater treatment plants, that can also cause respiratory diseases. With so much immunosupressive treatments around, we have created wonderful opportunities for fast evolving patogens. What is your opinion? and about antibiotics resistant mutants? Are we doomed? I mean of course we are doomed, but how soon?
Even if new diseases are coming up, there are a lot of social things we can do to mitigate that risk. For example, I was talking to a retail pharmacist who says their business dies off in the summer because the kids aren’t spreading disease in schools. So get rid of schools as we know them (hundreds of kids in one building), and there goes one of nature’s petri dishes. Sort of like who sanitizing water put an end to cholera in countries that sanitize water.
It’s not something i’d ever noticed before but the lack of mention of disease as the cause of failed campaigns in Roman history (at least to my memory) is a dog that didn’t bark when you compare it to how often disease is mentioned as a critical factor in medieval military history.
Roman military medicine was well developed. They had military hospitals. The camps were well planned and spacious. Discipline was severe. And the soldiers were young.
Yes but my guess is the critical thing was the “camps were well planned” part, especially regarding the basics e.g. latrines, hygeine and water supply – but also maybe having fewer contagious diseases to start with?
It might be an interesting study for someone who knew a lot about Roman military history – if the Romans ever did have notable disease problems on particular campaigns which campaigns they were and *where* they were.
I noticed it. It’s not absolute: disease sometimes was a factor in Roman campaigns, but not often.
Generally you have to knowa lot of facts about a subject before you can notice the non-barking dogs. That would make for some interesting posts.
I’m no expert, but the first mention I can remember of disease affecting a Roman military campaign was in 170 AD, in Marcus Aurelius’ operations in Germania.
Crusaders died faster than they could reproduce when they attempted to occupy the holy land. Yet the Roman army occupied the entire area without problems. Written history does a very poor job of reporting how unimportant people died. It would be nice to read a history book reporting on the impact of diseases that draws upon skeletal evidence rather than what little we have that was written down.
“Written history does a very poor job of reporting how unimportant people died.”
True but medieval history is full of sieges – important people history – that had to be called off because of disease in the camp.
Yes, but the land was different. In Roman times, Israel was well developed, fully cultivated and densely populated. The Arab conquest destroyed the drainage and irrigation systems, and the land became a desert in the South and a malarial swamp in the North and the Coastal areas. The first Jewish settlers in the 19th century also died like the Crusaders , till the Coastal swamps were regulated. In Herzliya there was a large swamp left (called the Bassa) – recently we discovered an ancient “Roman” drainage tunnel that had become silted and forgotten long time ago. The Romans were excellent engineers, and in parts of their empire (like North Africa) the sanitation was better in their times than today.
I’m not so sure. It’s hard to make accurate populations estimates for Classical times. Nor I do I think that Israel had any large-scale irrigation back then, although I could be wrong.
More generally, I see several factors that one would need to get straight in order to make such estimates. First, has the land been degraded – meaning stuff like erosion, salinization, deforestation, etc. I guess I’d include exhaustion of ground-water – the Garamantes depended upon fossil water and the kingdom disintegrated when they ran out.
Second, how productive were the old-timey farming methods, using old-timey varieties of domesticated plants? Using old-timey pest-control methods? Next, has there been relevant climatic change?
You’d need to understand those before you could really determine the extent to which some particular people messed up agriculture. My general impression is that the original Arab conquest didn’t much hurt agriculture in the Middle East, while the irruption of Bedouin tribes into North Africa did, along with full use of the camel. While the Mongols came close to ruining everything, in Iran and Iraq.
Lastly, I have the impression that the Ottomans blighted everything they touched, intentionally on the frontier, accidentally in the interior of the Empire.
But I could be wrong.
What about the reports of signs of syphilis in bodies from Pompeii proving that it was an Old World disease?
http://www.bbc.co.uk/news/world-europe-11952322
Were these reports in error?
Almost certainly in error. The molecular evidence is pretty clear.
There was a long-drawn-out controversy about the origin of syphilis (American or not?) and as far as I’m concerned, it confirms that an awful lot of people genuinely enjoy being wrong.
What did the Romans use for toilet paper?
Sea sponges on a stick.
Rare cancer seen among homosexuals but this was from more than 30 years ago.
The increase in disease is often argued as a cause of the collapse of Rome, but it just now occurs to me that it could also answer the equally interesting question of why Rome didn’t reform (unlike China).
First, if disease lowered population densities and made urbanization more difficult, that would have limited centralization. But more importantly, if disease attacked massed armies, it would have pushed towards military decentralization.
re-form.