Salting the earth

At the end of that space, a second Scipio, the son of Paulus Aemilius, the conqueror of Perseus, took the city by storm, and destroyed it, razing it to the ground, passing the ploughshare over its site, and sowing salt in the furrows, the emblem of barrenness and annihilation.

-- The New American Cyclopaedia, vol. 4 (1858) p. 479

The setting: the Romans are sacking Carthage in 146 BCE. Supposedly the Roman general Scipio Aemilianus salts the earth to eradicate Carthage for good, making a fertile land into desert.

The destruction wrought by the Romans was absolutely real, and truly horrific: Appian's account of it is real nightmare fuel. The salting-the-earth story, though, is pure myth. There isn't a shred of ancient evidence to suggest that it happened. The story didn't appear until the 1800s.

The myth evaporates easily enough. But it's still a very interesting topic. For one thing, there was such a thing as ploughing over a city and salting the earth -- it's just that it didn't happen to Carthage.

For another thing: when we look closely, it turns out 'salting the earth' isn't about destroying fertile land and turning it into desert. Oh no. The salt is actually meant to be a fertiliser.

Confused? Read on.

Giovanni Battista Tiepolo,
The capture of Carthage (1729; NY Met)

Even some professional ancient historians believed the salt myth until the late 1980s, when it got torn to shreds by a cluster of articles in the American journal Classical Philology. First, in 1986, an article by R. T. Ridley dismantled the myth and criticised scholars who had helped perpetuate it. The earliest example Ridley could find was in a volume of the Cambridge Ancient History from 1930. In 1988 another three authors -- including one Ridley had criticised, B. H. Warmington -- added afterthoughts to Ridley's article (plus an apology in Warmington's case). Between them, they managed to push the date of the salt myth back to an essay published in 1905.

One of them, S. T. Stevens, argued that the myth was an extension of the symbolic act of ploughing the land when founding a city (widely attested) or destroying it (attested in one Greco-Roman source). Long before the salt myth came along, it had been widely believed that Carthage had been ploughed over. Now, the ploughing myth has no foundation either. But it pops up in some eminent historians in the late 1800s; it also appeared in the 3rd edition of the Encyclopaedia Britannica, vol. 4 p. 215, in 1797, and was repeated verbatim until at least the 6th edition in 1823.

In fact the ploughing myth goes back a lot further. In 1299 Pope Boniface VIII personally reported how he demolished the city of Palestrina, as part of his feud with the Colonna family, as follows: 'I subjected it to the plough, following the example of Carthage of old in Africa'. He goes on, 'we also made salt in it, and commanded that it be sown over, so that it should have neither the condition, nor name, nor title of a city.' There are strong connections between the ploughing myth and the salt myth: we'll see more about these connections below.

So the ploughing myth goes back at least to the 13th century. What about the salt myth? Moving on to the internet age, and Wikipedia, we find that it has now been pushed back to 1863. In fact it's a little older still: its earliest appearance is indeed in Ripley and Dana's New American Cyclopaedia, but the volume with the 'Carthage' article dates to 1858 (see link at top).

Most observers agree that the modern idea of salting the earth is inspired by an incident in the Hebrew Bible, in Judges 9:45, where the Israelite king Abimelech 'razed the city and sowed it with salt' at Shechem.

Cover of the 2012 album
Salt the Earth by Carthage,
a deathcore band based in Maryland

In 2007 The Straight Dope covered the myth. There, Cecil Adams tried to estimate how much salt you'd actually need to make land effectively infertile. His estimate: 31 tons per acre. This works out to 7 kg per square metre, or a coating of about 6 mm. In the 3rd edition Britannica and the New American Cyclopaedia, Carthage's walls supposedly had a perimeter of 23 miles (37 km). I haven't tried to find out where they got this factoid from. But assuming they're right, that limits its area to 109 square km. The amount of salt required to make it infertile, then, could be up to 7.63 × 10⁸ kg, or 763,210 tonnes. Standard Roman merchant ships in the Republican era could carry between 70 and 150 tonnes. So to transport this much salt you'd need a fleet of somewhere between 5000 and 10,000 ships, all packed to the brim with salt.

Here endeth the myth. All nice and tidy. There is a little more to talk about, though. And you know what happens when we get into the details ...

First: given that you'd need such a vast quantity of salt to make a place infertile, why then do we find 'salting the earth' going on in the bible, and in Pope Boniface's misdeeds at Palestrina? And second: if it turns out that they're not literally making the area devoid of life, what is really going on?

Ploughing and salting in the ancient Near East

Parts of the answer to the first question can be found in the Wikipedia article I already cited. There's a handful of parallels in mediaeval accounts. But much more interestingly, there's a whole set of parallels for ploughing over cities and salting the earth in several ancient Near Eastern sources. Here they are, all reported by Ridley (1986: 145):

• a record of the proto-Hittite king Anitta of Nesa (ca. 1720 BCE), who destroyed the city of Hattusa and sowed it with weeds ('and in its place I sowed weeds', pe-e-di-is-si-ma ZÀ.AH-LI-an a-ne-e-nu-un; source. Dörfler et al. 2011: 113-14 interpret the weeds as a bioweapon, suggesting that they might have been bearded darnel, which can devastate wheat production, or greater dodder, which destroys legumes and survives for years in fallow soil);
• an inscription where the Assyrian king Adadnirari I (early 1200s BCE) destroys the city of Taidu and strews something called kudimmu over it, a plant whose identity is unknown but which may be linked with salt somehow;
• another Assyrian inscription where Shalmaneser I (mid-1200s BCE) destroys Arinu and strews kudimmu over it;
• another (Grayson, Assyrian Royal Inscriptions vol. 2 no. 238) where Tiglath-Pileser I (early 1000s BCE) destroys Hunusa and strews something called sipu-stones over it;
• another where Ashurbanipal (600s BCE) destroys Elam and scatters it with salt and sahlu seeds, where sahlu is an unknown plant;
• the Hebrew bible, Judges 9:45, written in the 7th century BCE, reporting how Abimelech destroyed the city of Shechem: 'he razed the city and sowed it with salt';
• and the latest parallel, again in the Hebrew bible, Jeremiah 26:18: 'Zion shall be ploughed as a field; Jerusalem shall become a heap of ruins, and the mountain of the house a wooded height.'

Most of the mediaeval and modern examples owe a lot to the incident in Judges 9. But the blend of salting and ploughing is not a modern invention. It wasn't invented by Pope Boniface VIII either.

Salt = fertiliser

In the Hebrew bible, salt is regularly a symbol of barrenness: see Deuteronomy 29:23, Jeremiah 17:6, and Psalm 107:34. Yet in the other ancient testimony cited above, it's strikingly clear that the salt is not meant to make the soil infertile. Ashurbanipal uses both salt and seeds; Judges 9:45 specifies that the salt is sown (וַיִּזְרָעֶהָ), not dumped in a layer.

Boniface, too, clearly meant his ploughing-and-salting at Palestrina to have fertile results. His exact words were

ac salem in ea etiam fecimus & mandavimus seminari

and we also made salt in it, and commanded that it be sown over

-- bull of 1299, section 6

In the 21st century, and back in the 20th century too, most of us are accustomed to thinking of salt as something that eradicates life. If soil is too saline, nothing will grow in it. This is going to be especially on your mind if you're thinking of places like the Dead Sea, or the Bonneville Salt Flats in Utah: both of them salty as all hell, both iconically barren places.

Will Smith drags an alien across the Bonneville Salt Flats
(Independence Day, 1996)

In fact, salt was regularly used as a fertiliser in the past. You have to be much more careful with it than with other fertilisers -- too much will kill off the plants, it only works for some plants, and you don't put it on the roots (according to ancient sources, at least) -- but within those limits, it has been used regularly and, it may well be, very effectively. Plants need salt too. Even in the modern era, there were many experiments with salt as a fertiliser in the 1800s (examples: 1, 2, 3, 4). And yes, we're talking specifically about sodium chloride, not Epsom salt or saltpetre.

Nowadays salt has mostly gone out of fashion. Soil salinity is a real problem. Growers in the past may have had success with salt, but it is really really easy to overdo it. It does still see some use: some cattle farmers use it for growing feed, as cows need a lot of salt. Some organic farmers use it too. But before you try this in your own garden, check the salinity of your soil first.

On to the actual testimony. Greco-Roman witnesses have a fair amount to say on the subject. First, Theophrastus' On effects in plants:

Still, saline water is beneficial even for some vegetables, as cabbage, beet, rue and rocket, ... This improvement occurs, and in a word salinity is good for these vegetables, because they have a certain bitterness in their natures, and the salt water, by penetrating the plants and as it were opening outlets, extracts it (which is why cabbage is best in briny soil) ...

-- Theophrastus De causis 2.5.3-4 (tr. Einarson and Link)

And again:

We said earlier that salinity is also suited to some vegetables, and that soda is used with others. And so it seems we must accept the salinity here too [in pomegranate and almond trees] as appropriate to the plants, since it is evident that the sweetness of these vegetables comes from the saline water and the food.

-- Theophrastus De causis 3.17.8

Elsewhere he repeats that cabbage and purslane grow sweet and have little bitterness in saline soil (De causis 6.10.8); and he claims Egyptian olive oil isn't as good as the Greek stuff because it doesn't get enough salt (Historia 4.2.9).

But he really goes all out when it comes to date palms. Ancient date growers didn't just add a few grains of salt, according to Theophrastus. To borrow a phrase from Quentin Tarantino, they drowned 'em in that shit.

(The date palm) likes a soil which contains salt; wherefore, where such soil is not available, the growers sprinkle salt about it; and this must not be done around the actual roots: one must keep the salt some way off and sprinkle about a hēmiekton (i.e. about 4.3 litres; ca. 5 kg). ... When the tree is a year old, they transplant it and give plenty of salt, and this treatment is repeated when it is two years old, for it delights greatly in being transplanted.

-- Theophrastus Historia 2.6.2-3 (tr. Hort, adjusted)

Elsewhere he mentions that Babylonian date growers use salt but no manure for their fertiliser, and that another method of application is manually applying lumps of salt to the trees (De causis 3.17.1-4; also Historia 4.3.5). Theophrastus' experience must have been with very salt-starved soil. Modern research has shown that date palms do tolerate relatively high salinity, but as with anything, that tolerance has limits. According to this 2015 study, the limit is around 9 to 12.8 dS m^-1 (roughly 6-8 g per litre of soil). Modern date growers don't use salt as a fertiliser, even in the region that was once Babylonia.

Theophrastus' enthusiasm about salt isn't quite as visible in other ancient sources. They do mention it though. Pliny the Elder comes up with a rather imaginative explanation -- he obviously doesn't have as much growing experience as Theophrastus --

salsaeque terrae multa melius creduntur, tutiora a vitiis innascentium animalium.

And many (plants) are better entrusted to salted earth, as they are safer from being harmed by animals breeding there.

-- Pliny, Natural history 17.29

Pliny is also aware that cattle, sheep, and yoke animals love salty pastures, and that the salt improves their milk and cheese (Nat. hist. 31.88).

A much more striking allusion is in the New Testament, in the gospel of Luke.

καλὸν οὖν τὸ ἅλας· ἐὰν δὲ καὶ τὸ ἅλας μωρανθῇ, ἐν τίνι ἀρτυθήσεται; οὔτε εἰς γῆν οὔτε εἰς κοπρίαν εὔθετόν ἐστιν· ἔξω βάλλουσιν αὐτό.

Salt is good; but if the salt goes bad, in what how will it be used for seasoning? It isn't suitable for the ground or for a manure heap. They throw it away.

-- Luke 14:34-35 (my translation)

As with almost anything in the New Testament, I need to add a caution. These verses are paralleled in Mark 9:50 and Matthew 5:13, but those passages aren't as clear about the use of salt as a fertiliser. As a result, New Testament scholars tend to debate the meaning of the passage in Luke.

Digression: there are two other translation problems here, though neither of them has an impact on the bit about using salt as a fertiliser. I mention them because they are bugging me.

1. ἐὰν ... τὸ ἅλας μωρανθῇ is more conventionally translated as 'if the salt loses its taste'. That translation is driven by the parallel in Mark, which does mean something like that: ἐὰν δὲ τὸ ἅλας ἄναλον γένηται, 'if the salt becomes unsalty'. But Matthew and Luke use the verb μωραίνω, in the passive, which elsewhere always means 'become μῶρος, become foolish, be stupefied'. There are no parallels to suggest it can ever mean anything like 'lose its taste'. (μωραίνω is a moderately common word; just within the NT cf. Romans 1:22, 1 Corinthians 1:20.)
2. ἐν τίνι ἀρτυθήσεται is obscure. The verb ἀρτύω means 'to prepare, season, salt', so literally the phrase means 'In with what will (the salt) be seasoned?' My translation above, which takes ἀρτύω as 'to use as a seasoning', strains the syntax a bit. However, the conventional translation 'how can its saltiness be restored?' (NRSV) is much more of a stretch: interpreting ἀρτύω as 'to restore the taste of' is a strain on meaning, not just syntax, and ἐν τίνι cannot mean 'how' or 'with what'. [edit, much later: ἐν does indeed mean instrumental 'with' in New Testament Greek.]

The salt-as-fertiliser reading does however expose another allusion in the parallel in Matthew 5:13 'You are the salt of the earth' (ὑμεῖς ἐστε τὸ ἅλας τῆς γῆς). The idea there isn't just that people are flavoursome, and good for preserving foods -- they're also good for growing things!

So no, Carthage wasn't ploughed and salted, but some other places throughout history have been. It was indeed ecological warfare: the idea was indeed to eradicate a city forever. But not by eradicating all life. Rather, the idea was to turn a once-bustling city into a green space, covered in weeds. And for that purpose, you don't need an outrageous amount of salt at all.

References

• Dörfler, W; Herking, C.; Neef, R.; Pasternak, R.; von den Driesch, A. 2011. 'Environment and economy in Hittite Anatolia.' In: Genz, H.; Mielke, D. P. (eds.) Insights into Hittite history and archaeology. Leuven: Peeters. 99-124.
• Ridley, R. T. 1986. 'To be taken with a pinch of salt: the destruction of Carthage.' Classical Philology 81: 140-6.
• Stevens, S. T. 1988. 'A legend of the destruction of Carthage.' Classical Philology 83: 39-41.
• Visonà, P. 1988. 'Passing the salt: on the destruction of Carthage again.' Classical Philology 83: 41-2.
• Warmington, B. H. 1988. 'The destruction of Carthage: a retractatio.' Classical Philology 83: 308-10.