The Biblical Record
The first step is to establish what the Bible says about Sodom and Gomorrah. We get the story of the original cities in the book of Genesis, then, throughout the rest of the Bible, these cities are referred back to no less than twenty times as an example of how God punishes sin. At the end of the Bible (II Peter 2:6, Jude 7), Sodom and Gomorrah is the epitome of God's wrath against sin.
What was the sin of Sodom and Gomorrah?
The Jude passage mentioned earlier cites "fornication" and "going after strange flesh." The Genesis passages (ch. 18 & 19) mention the citizens wanting to molest visitors, then turning on Lot who was keeping the visitors safe. Jeremiah also seems to mention sexual sin (23:14) along with lying and "strengthen[ing] the hands of evil doers." The most detailed list of Sodom's sin is found in Ezekiel 16:49 (if indeed it is not speaking figuratively of another city); "pride" and "prosperous ease" head the list, followed by the converse of Jeremiah's complaint, they "do not strengthen the hand of the poor and needy," and finally, stating that they were "haughty" and "committed abomination before God." The magnitude of Sodom's sin is also mentioned throughout the Bible as "great and grievous" (Gen.18:20), so pervasive that Abraham doubted that there were even 20 righteous people in it (Gen. 18:32), and that they acted without shame, openly displaying their sin, not hiding it (Isa.3:9).
For the greatness of Sodom and Gomorrah's sin, God determined to punish them by wiping them out. He states His intentions on a visit to Abraham, then sends two angels to accomplish the destructive act (Gen. 18-19).
In the Biblical record we find a number of facts about the actual cities of Sodom and Gomorrah:
There were a series of five cities named Sodom, Gomorrah, Admah, Zeboiim, and Belar/Zoar (Gen. 10:19, 14:2, 14:8, Deut. 29:23, Hosea 11:8)
1.They were border cities of Canaan, in line with Sidon, Gaza, and Lasha (Gen. 10:19, 13:12)
2.They were visible to the East of where Abraham lived (Gen. 13:10, 18:16, 19:28), but not so close that a military threat to them would threaten Abraham (Gen. 14).
3.They were in the area of the Plain of the Jordan (Genesis 13:10-12)
4.They were well-watered, and contained lush greenery desirable to a shepherd (Gen. 13:10)
5.Sodom was large enough that 50 people would be a small percentage of its population (Gen. 18:26), but small enough that its army, when combined with that of the neighboring 4 cities, was inferior to Abraham's army of 318 men (Gen. 14). It doesn't matter if those citys had 1000's of army men, God Was With Abraham!
6.Commerce, agriculture--including wine-making--and building were carried out in Sodom (Luke 17:28, Deut.32:32)
7.Sodom had a city gate (Gen. 19:1), and Lot's house had a solid door (Gen. 19:6-11)
8.The battleground of choice for the allied armies of these five cities was "the Valley of Siddim, which is the Salt Sea." When they were defeated, they fled to "the mountain" leaving their villages to be plundered. They regrouped at the Vale of Shaveh (The King's Vale) which was apparently near modern Jerusalem, and welcomed a triumphant Abraham (Gen. 14).
9.The cities were destroyed by God quickly, in the space of a morning (Gen. 19:13-29, Lam 4:6, Amos 4:1, Luke 17:29)
10.The entire plain was destroyed with brimstone and fire from heaven. Smoke went up from it "like a furnace," and it was turned to ashes (Gen. 19:24,27, II Pet.2:6) Meaning any other Little Towns/Villages,Tribes or Trading Posts that might have been in the valley as well were also destoryed (besides) along with the 4 cities! All Animals & Plant Life in that area were also destoryed too!
11.The last city, Zoar, was a small city (Gen. 19:20), was closer to Sodom than "the mountain," (Gen. 19:19-20), and was not destroyed (Gen. 19:21&29)
12.There were no survivors to the other cities (Gen. 19:25, Isa. 1:9, Isa.13:19-20, Jer. 49:18, Jer 50:40, Zeph. 2:9)
13.Sodom was later identified with the city of Jerusalem (Isa. 1:10, Ez.16:55, Rev. 11:8), possibly because of the parallels of their sinfulness. Sodomy was a constant problem in Jerusalem (I Kings. 14:24, 15:12, 22:46, II Ki.23:7).
14.The ruined cities and the unoccupied wasteland around them could be seen by the Jews throughout Bible times: in Moses' day (Deut. 29:23), during the period of the Kings (Isaiah 13:19ff, Zeph. 2:9), and during the Exhile (Jeremiah 50:39ff).