In ancient and medieval cities, what events would occur when a city is sacked? Would attackers run about slaughtering and stealing as they wanted, or was there order amongst them? What would they look to steal, and how would it all be transported? What would they do to the city, would it be left or occupied?
This is all I have to ask for now, thanks in advance!
In ancient Greece, if you were in a city taken by siege, it was generally understood that you were not going to have a good time:
It is a law established for all time among all men that when a city is taken in war, the persons and the property of the inhabitants belong to the captors.
-- Xenophon, Education of Kyros 7.5.73
Greek authors rarely go into any detail when describing the fall of a city, so if we want to know what this really means, we are to some extent forced to use our imagination. However, it's clear from what little we hear that Xenophon's 'universal law' usually meant 3 things:
All movable property was taken
All adult men were killed
All women, children and elderly men were sold into slavery.
The first of these points is least well attested, but probably most widespread. Every warrior who was sent against an enemy settlement would hope to come away with a profit. Homes could be stripped of furniture and metal objects; temples could be robbed of their dedications and temple treasuries emptied. If there was time, even the rooftiles and wooden fittings of houses could be torn off and carried away. The simple fact that large amounts of ancient coinage and jewellry was preserved in its hiding place (buried, thrown into wells, etc.) shows that people were quite concerned to keep their valuables out of the hands of greedy invaders.
The second point is better known, because it was a matter of justice and pride. When a city was attacked, it could choose to surrender; if it did not, it forfeited any claim to mercy. Those who had decided to resist their enemies would get what they deserved. The most explicit example of this is the fate Agamemnon desired for Troy:
Not a single one of them must escape sheer destruction at our hands. Not even if a mother carries one in her belly and he is male, not even he should escape. All together they must be exterminated from Troy, their bodies untended and invisible.
-- Iliad 6.57-62
There are loads of examples from Greek history of sieges ending with the slaughter of all adult men. These massacres removed the defeated community's ability to fight and ensured that there would be no further resistance.
The third point arises from the fact that the Greeks seem to have considered it barbaric to kill captured women and children as well as men. The few examples of this in Greek history were condemned as savage. Once the needs of revenge had been satisfied, the remaining population was instead considered a potential source of profit:
When they were delivered to her by the Persians, Pheretime took the most guilty of the Barkaians and set them impaled around the top of the wall; the breasts of their women she cut off and planted around the wall in like manner. As for the rest of the Barkaians, she told the Persians to take them as plunder.
-- Herodotos 4.202
There was substantial money to be made from this, which is why commanders sometimes tried to restrain the bloodlust of their victorious troops. Even if it was just, as well as satisfying, to kill the defenders, it still amounted to the destruction of a source of income:
Dionysios' entire army burst into the city (...) and now every spot was a scene of mass slaughter; for the Sicilian Greeks, eager to return cruelty for cruelty, slew everyone they encountered, sparing without distinction not a child, not a woman, not an elder. Dionysios, wishing to sell the inhabitants into slavery for the money he could gather, at first attempted to restrain the soldiers from murdering the captives, but when no one paid any attention to him and he saw that the fury of the Sicilian Greeks was not to be controlled, he stationed heralds to cry aloud and tell the Motyans to take refuge in the temples which were revered by the Greeks. When this was done, the soldiers ceased their slaughter and turned to looting the property.
-- Diodoros of Sicily 14.53.1-3
The beginning of this passage is unique in actually describing a scene that must have been typical when a city fell to a Greek army. Most successful siege assaults were not the result of elaborate circumvallation, but of a surprise assault or betrayal. As a result, rather than bottling up the helpless enemy from all sides, the attackers usually entered the city from one point and began their rampage from there. Those left in the city therefore had two choices: either to resist or to flee. The former would result in the brutal fate sketched above - but the latter explains how Greek communities often seem to have survived a lost siege despite the genocidal intent of their attackers. It was often possible for a substantial part of the population to get away.
Their ultimate fate would then depend on what the victorious enemy intended to do with the settlement. Sometimes (especially in the Archaic period) their intent was to seize the territory for themselves; in these cases the town would be razed, and the fugitive population cast adrift. Fear of this outcome was supposed to keep the Spartans in the fight against the Messenians early in their history:
The most wretched of all things is for a man to leave his city and its fertile fields, reduced to the life of a beggar, wandering with his mother and aged father, his little children and wedded wife. Wherever he ends up, he will be as an enemy dwelling among them. He will succumb to need and detestable poverty, bring shame upon his family, disgrace his splendid looks. All forms of dishonour and misery will dog him. Since this is how it is and no one cares for or respects a wanderer or his offspring at all, let us fight hard for our land and die for our children without sparing our lives.
-- Tyrtaios fr. 10.3-14
If they had friends elsewhere, they might be able to obtain a temporary home, or even gain resident status and a home away from home, as the Plataians did at Athens when the Spartans razed their settlement in 427 BC.
In the Classical period, the intention was often rather to plant settlers on the conquered territory in order to expand the victorious city's number of land-owning citizens. This is what Athens did with the land of most of its defeated enemies from 506 BC onward. In such cases, the captured city might be reinhabited - at times by the new settlers along with the old population of women and children, whom they took as wives or slaves.
Alternatively, once due vengeance had been exacted, the remnants of the city's population could simply be allowed to return to it, often subjected to tribute and an imposed political regime. When the Athenians finally lost their fleet at Aigospotamoi in 405 BC, fear washed through the city, because the Athenians fully expected to meet the same fate that they had inflicted upon other Greeks throughout the decades of their Empire - the eradication of their community, the death of their men, and the sale of their women into slavery. However, for reasons that are still debated today, the Spartans decided to spare them. They got away with "only" a sack, the destruction of their walls, and the imposition of the tyrannical yoke of the Thirty.
Follow up question: was the sacking/genocide/mass murder of Carthage an unusual occurrence or where there any other such gigantic mass killings of entire populations in pre-modern times?