Sodom and Gomorrha
Two cities of the Pentapolis, utterly destroyed by "brimstone and fire from the Lord out of Heaven" (Genesis 13, 18, 19), for the unnatural sins of their inhabitants.
Their names are synonymous with impenitent sin, and their fall with a manifestation of God's just wrath (Deuteronomy 29; 2nd Peter 2; Jude 7; Ezechiel 16).
Tradition says their site is covered by the Dead Sea, but geologically this is impossible; the exact location is unknown, but is included in "the country about the Jordan."
New Catholic Dictionary