Rape, plunder and murder were the “normal” side effects of war in pre-modern times (and, in some geographical areas, it is still the case; the atrocities depicted in Sud Kivu are not very different from what you could expect from armed bands). Ancient armies behaved exactly in the same fashion — and examples like that of the post-WW2 reconquest of Germany, especially by the Red Army (even though (edit) Western Allied forces are not innocent either), show that it was not inexistent either in 20th century Europe.

Biblical texts give us a good idea of the consequences of a lost war in the Ancient Middle East — Dt 21:10-11 (NIV) is pretty explicit: “When you go to war against your enemies and the Lord your God delivers them into your hands and you take captives, if you notice among the captives a beautiful woman and are attracted to her, you may take her as your wife.” Similarly, Moses (Num 31), in a fit of pacifism: “Now kill all the boys. And kill every woman who has slept with a man, but save for yourselves every girl who has never slept with a man.” As for the Greeks, well, the Iliad starts with a dispute over Briseis, a war captive (whose consentment is not exactly the main preoccupation of Achilles and Agamemnon); later on, the rape of Cassandra by Ajax becomes a problem, not because of the act in itself, but because it happens in a temple. There is even a famous Greek vase, the Eurymedon vase, which has sometimes been interpreted as evidence of male on male rape. Romans were not better, and I think that Liv. 29.17.15 speaks for itself: “They all rob, plunder, beat, wound, slay. They defile matrons, maidens and free-born boys, dragged from the embrace of parents” (speech of a man from Locri, an Italian city that had the bad idea of rejoining Hannibal).

Then, the question could be: was warfare more prevalent in the Middle Ages than in Antiquity? Such a comparison would probably be very hard to do. However, I am inclined to think that Antiquity might have been a more dangerous time in some ways — civic levies created a great number of important armies, whereas medieval forces, especially when political fragmentation was at its highest point, were pretty small. There might have been a greater number of low intensity conflicts, but war was in many ways less “total” than during the Antiquity (you will not find many examples of cities being sacked, its entire population killed or enslaved, in the 11th century).

It's true, to varying degrees and in various ways. There was quite a bit of pillaging and looting during the Hundred Years' War, but largely it was the result of national policy. The image most people have of the middle ages is that of the period 900-1100. This was a period of governmental collapse and decentralization, where most power passed to the local level, and many, perhaps most, castellans were independent rulers in all but name, administering an area 10-20 miles from his castle. That level of decentralization led to a chaotic state of affairs, with endemic war between feuding neighbors and relatives. Much of this warfare involved attacking an enemy's economic supports, his land and his labor. It apparently got bad enough that, as part of the Peace of God movement, Gunbald, Archbishop of Bordeaux, together with his bishops, issued the following at the Synod of Charroux in 989.

1. Anathema against those who break into churches. If anyone breaks into or robs a church, he shall be anathema unless he makes satisfaction.

2. Anathema against those who rob the poor. If anyone robs a peasant or any other poor person of a sheep, ox, ass, cow, goat, or pig, he shall be anathema unless he makes satisfaction.

3. Anathema against those who injure clergymen. If anyone attacks, seizes, or beats a priest, deacon, or any other clergyman, who is no . t bearing arms (shield, sword, coat of mail, or helmet), but is going along peacefully or staying in the house, the sacrilegious person shall be excommunicated and cut off from the church, unless he makes satisfaction, or unless the bishop discovers that the clergyman brought it upon himself by his own fault.

Oliver J. Thatcher, and Edgar Holmes McNeal, eds., A Source Book for Medieval History, (New York: Scribners, 1905), p. 412

Edit. Whoever presented me with this gift of gold, know that it is appreciated, if entirely unexpected.

I'd also like to add that the worst was when a siege was broken. The longer the inhabitants tried to hold back the siege, the worse the looting. Rape, pillage, etc. was all normal for 2-3 days after.

This was done for a number of reasons and was considered a completely legitimate method of warfare. 1) To warn the next city against holding out so long, 2) to reward the attacking troops for hard work.

Another downside was that if a city surrendered too quickly, so as to avoid the pillaging, if the original lord retook the city then he would allow his troops to rape and pillage as punishment for surrendering too quickly. It was a real double-edged sword for people in the cities.

Then, some wars were worse than others regarding rural areas. The Thirty Years War was particularly bad, as the armies ran out of funds and the generals decided that instead of paychecks, they would just let their men forage and rape and pillage the entire countryside.

It really wasn't until the conclusion of the Thirty Years War that simply being in an army wasn't a free license to rape and pillage. It's about this time that Hugo Grotius began codifying secular laws of war to try to protect non-combatants.

There's a lot of good answers in this thread, but I'm curious if anyone can speak to ancient Chinese warfare?