It used to be thought that the Greeks were notably restrained in their wars against each other. The traditional view on Greek warfare was that it was shaped by a common desire to reduce its human and economic cost; it was an affair only of warriors, who would fight until one side broke and ran, and then promptly declare victory. Tacit rules kept them from pursuing and killing the enemy, attacking their settlements, or harming any men they had taken prisoner.

Recent scholarship has adjusted this view. Or really, I should say: recent scholarship has made a 180 on this point. Here's Adriaan Lanni, writing on the laws and customs of Greek warfare in 2008:

Nothing, least of all compassion and mercy in battle, was owed to the soldiers or citizens of enemy states.

Lanni's words are in line with the conclusions of a number of scholars who have recently re-examined the issue (references below). It is now widely understood that much of ancient Greek morality, as our sources preserve it, comes down to a simple rule for life: "help your friends and hurt your enemies." Practically anything that fit within this rule, with the exception of sacrilege or breaches of the law, was considered morally just. This included doing the absolute maximum possible damage to enemy armies both on and off the battlefield. While there were some reservations regarding the killing of captured women and children, warriors taken prisoner in battle were at the complete mercy of their captors, and no observer would raise moral objections to their murder.

The point about the law is significant, though. Several surviving texts seem to argue that the killing of prisoners would be against the "laws of the Greeks" or the "common laws" - unwritten but universally understood conventions that allowed affairs between Greek states to run smoothly. These customs included the inviolability of heralds and messengers, as well as the ban on hostilities during a sacred truce, such as during the Olympic Games. Some texts argue that protection of prisoners, too, was a general custom that victorious forces ought to observe. This is the main reason why earlier scholarship assumed that such a rule really existed, and was honoured, at least until the time of the Peloponnesian War.

Yet there is no actual evidence of such a law. The argument is always presented as one side in a debate, with the opposing side arguing - without being presented in any sense as the villain - that the prisoners do not deserve mercy. Indeed, the argument typically isn't that prisoners always ought to be spared, but that they ought to be spared either because their captors swore to do so, or because their surrender placed them under sacred protection as suppliants. In other words, the "common law" that was invoked to save the lives of prisoners wasn't that prisoners shouldn't be killed, but that one shouldn't offend the gods by breaking solemn oaths. As with other supposed restrictions on Greek warfare, it turns out that the only real offence was one against the gods. In the case of the prisoners' defence, inevitably, the captors would simply argue that no such oaths were taken, and that the prisoners are therefore at their mercy. As John Dayton put it, if a victorious army wished to kill its prisoners, "no Hellenic law stood in the way."

But if killing prisoners was not considered beyond the pale, why would anyone ever surrender? The answer is that just because the winners of a battle might execute prisoners without facing moral, legal or divine backlash, doesn't mean that they would. While we have plenty of examples from the sources of prisoners being murdered, this doesn't mean that this outcome was guaranteed. In practice, there were 4 options, in ascending order of severity:

• Captives were ransomed for a fixed sum per prisoner.

• Captives were sold into slavery.

• Captives were mutilated and sold into slavery.

• Captives were killed.

With this list of possible outcomes, it's understandable that Greek armies tended to flee rather than surrender. Even so, at least 3 of these options are arguably preferrable to certain death. While prisoners were sometimes subjected to a combination of options (such as the thousands of Athenians captured in Sicily in 413 BC, of which the generals were executed and the others starved out before the remainder were enslaved), the first two were common enough to be expected by those who surrendered. Herodotos claims that the Peloponnese in the early 5th century BC had an agreed system in which war captives were sold back to their home states for 200 drachmai per man (Hdt. 6.79.1), although no other agreement like this is known, and ransoming was not as common elsewhere. Enslavement was frequent, because it had the benefit for the victor of bringing in money. In some cases (as with some Athenian survivors of the Sicilian Expedition), this could work as a sort of roundabout ransoming, as relatives would buy their own kin back through the slave market. In other cases it would mean only that survivors would at least escape with their lives. The fact that arguments over what was to be done with captives are even recorded suggests that there was at least some consideration of mercy as a positive good, even if it did not go so far as to question the dominant morality. Lenience could at least make the victors look good, and might make the defeated state more favourably inclined.

In all, it's easy to imagine why we don't often hear of prisoners taken in battle, and why prisoners of war were more frequently taken in sieges and naval warfare (where crews of captured ships were unable to escape their fate). There were no rules protecting warriors from the most brutal treatment, and no distinction was made on that point between citizens, freeborn non-citizens, or slaves. Ultimately, what happened to captives was up to their captors, who made their decision on the basis of moral and strategic considerations that would vary from case to case.

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Sauces

P. Krentz, 'Fighting by the rules: the invention of the hoplite agôn', Hesperia 71.1 (2002) 23-39

J.C. Dayton, The Athletes of War (2005)

A. Lanni, 'The laws of war in ancient Greece', Law and History Review 26.3 (2008) 469-489

H. van Wees, 'Defeat and destruction: the ethics of ancient Greek warfare', M. Linder/S. Tausend (eds.), Böser Krieg (2011) 69-110