Sodom

But before they lay down, the men of the city, even the men of Sodom, compassed the house round, both old and young, all the people from every quarter: And they called unto Lot, and said unto him, Where are the men [angels] which came in to thee this night? bring them out unto us, that we may know them. (KJV)

Based on this incident it is often postulated that the sin was homosexuality and rape. However, it should be noted that the events that form the basis of this claim only occur in the narrative after God has already passed sentence on the cities -- God could not have been condemning Sodom for its treatment of Lot's guests themselves.

In contrast, the biblical book of Ezekiel holds that the crimes were economic, and not sexual.

As I live, says the Lord God, your sister Sodom and her daughters have not done as you and your daughters have done. This was the guilt of your sister Sodom; She and her daughters had pride, excess of food and prosperous ease, but did not aid the poor and needy. They were haughty and did abominable things before me; therefore I removed them when I saw it. Ezekiel 16:46-50

The view of Josephus

A Jewish tradition, described in the Mishnah, postulates that the sin of Sodom was related to property: they believed that "what is mine is mine, and what is yours is yours" (Abot), which is interpreted as a lack of compassion. It should be noted that the statements in the Mishnah and in the midrash literature are not always based on the literal meaning of the text, and often are considered to have little historical basis. However, they do provide us with information on what Jews of that era believed.

One tradition is that these five wealthy cities violated the Law of Hospitality: there is a series of legends regarding Sodom's hospitality, but these are apparently borrowed from Greek mythology. One example is the story of the "bed" that guests to Sodom were forced to sleep in: if they were too short they were stretched to fit it, and if they were too tall, they were cut up. This is an adaptation of the Greek myth of Procrustes.

The men of Sodom waxed haughty only on account of the good which the Holy One, blessed be He, had lavished upon them...They said: Since there cometh forth bread out of (our) earth, and it hath the dust of gold, why should we suffer wayfarers, who come to us only to deplete our wealth. Come, let us abolish the practice of travelling in our land.

There were four judges in Sodom named Shakrai (Liar), Shakurai (Awful Liar), Zayyafi (Forger), and Mazle Dina (Perverter of Justice). Now if a man assaulted his neighbour's wife and bruised her, they would say to the husband, Give her to him, that she may become pregnant for thee. If one cut off the ear of his neighbour's ass, they would order, Give it to him until it grows again.

Rabbi Ze'era said: The men of Sodom were the wealthy men of prosperity, on account of the good and fruitful land whereon they dwelt... Rabbi Nathaniel said: The men of Sodom had no consideration for the honour of their Owner by not distributing food to the wayfarer and stranger, but they even fenced in all the trees on top above their fruit so that so that they should not be seized; not even by the bird of heaven... Rabbi Joshua... said: They appointed over themselves judges who were lying judges, and they oppressed every wayfarer and stranger who entered Sodom by their perverse judgment, and they sent them forth naked...

The historical existence of Sodom and Gomorrah is still in dispute by archaeologists, with some believing they never existed, some believing they are now under the Dead Sea, and others claiming that they have been found (under other names) in the region to the southeast of the Dead Sea. Evidence has been found of towns in the region being ravaged by earthquakes, and some scholars have suggested that the abundance of sulphur in the region could account for the description of fire and brimstone raining down.