Babylon was the capital and chief city of the ancient Babylonian Empire.
Not long after the Assyrians conquered the Kingdom of Israel, the Assyrian Empire began to crumble. Meanwhile, the Chaldeans and Babylonians began to gain strength. In 609 B.C. the Babylonians, in league with Egypt and Media, conquered Nineveh, the capital of Assyria. The Babylonian king at the time was Nabopolassar. Nebuchadnezzar was his son. The Babylonian Empire reached the height of its splendor and power under Nebuchadnezzar, who became king upon the death of his father. Using captive slaves from his conquests, Nebuchadnezzar launched into a building program that made the capital city of Babylon the greatest city in the world.
The City of Babylon
Built on the Euphrates River, Babylon is reputed to be one of the largest and most magnificent cities of all time. Through conquest and commerce, the wealth of the world flowed into its treasuries. Jeremiah called it "the praise of the whole earth" (Jeremiah 52:41). Isaiah called it the "glory of kingdoms" (Isaiah 13:19). Archaeologists have found that the walls of Babylon were 23 feet thick, and made of baked brick and asphalt. Inside the walls was a filling of sand extending 69 feet, with an inner retaining wall 44 feet thick. The bricks of the wall were decoratively painted in beautiful colors. These walls encircled the entire city, about 14 miles on each side, or 56 miles.  (In contrast, Jerusalem's walls encompassed about a square mile.)
The city was reknowned for its beauty, especially for the "hanging gardens" created by King Nebuchadnezzar for his wife. These hanging gardens were considered one of the seven wonders of the ancient world. The Persian Princess, Amytis, who became Nebuchadnezzar's wife, was from a mountainous region of Persia, and found the flat, arid region of Babylon depressing. Nebuchadnezzar created an artificial mountain for her, 400 feet on each side. The mountain was terraced and rose 300 feet, visible above the walls of the city. The terraces of the mountain were contstructed on piers, with stairs from terrace to terrace. Each tier was enclosed by a wall 22 feet thick. On each terrace was a garden. The tops of the piers were overlaid with stones 16 feet by 4 feet. On the stones were layered matting, bitumen, two courses of bricks sheathed with lead, a depth of soil able to accommodate the roots of pine trees, and hollow piers filled with mold. Water from the Euphrates flowed near the mountain, and it was lifted by machinery up to the terraces. The woods seemed to overhang the mountain in levels; thus the nomer, "hanging gardens." 
The Wickedness of Babylon
The citizens and rulers of Babylon were wicked in the extreme. Babylon was a center of iniquity, carnality, and worldliness.  Will Durant wrote that "even Alexander, who was not above dying of drinking, was shocked by the morals of Babylon."  Fallows said that the inhabitants were "addicted to self-indulgence and effeminacy." Curtius says that the "rites of hospitality were polluted by the grossest and most shameless lusts," that money "dissolved every tie," and that all the enjoyments that accompany drunkenness were commonplace. 
Babylon stood in opposition to Israel and to righteousness. In three seiges, each one more violent than the one before, Babylon overtook Jerusalem and the Kingdom of Judah, and carried away its best and brightest citizens, while slaughtering others. The Book of Mormon account tells of a few who escaped to the American continent: Mulek, a son of King Zedekiah, and his associates; and Lehi, a prophet in Jerusalem, and his family and associates.
Judah was caught in a power struggle between Babylon and Egypt. Before the captivity, Judah was beholden to Egypt and paying heavy taxes. Babylon defeated Egypt at Charchemish in 605 B.C., and Judah became a vassal of Babylon. Jehoaikaim paid tribute to Babylon for three years before trying to free Judah. He was killed by the Babylonians at the first siege and exile of the most talented people in Judah. Through successive kings, Judah's rebellious spirit rose along with its wickedness. The Lord brought destruction upon Judah through conquering Babylon, which attacked Jerusalem after devastating the rest of the nation. The effect of the sieges were worsened by drought, which caused crops to fail and wild animals to invade the villages. 
Babylon as a Symbol of Wickedness and Worldiness
Inspired men in New Testament times applied the name Babylon to any force determined to spread spiritual confusion or darkness. (See Revelation 17; 18; Doctrine and Covenants 29:21; Ezekiel 38; 39.) The Doctrine and Covenants uses the term Babylon as a name for the wickedness of the world. (See Doctrine and Covenants 1:16; 35:11; 64:24; 133:14.)
The Fall of Babylon
Babylon fell suddenly to the Persians, reaping utter destruction. The golden age of the empire was short-lived—just over seventy years. When Christ comes again to rule on earth, "Babylon" will again fall, this time forever. All wickedness will be utterly destroyed when He comes. (See Second Coming.) Today, the Lord's servants are calling people to come forth out of Babylon, repent, and be saved. As it says in the Book of Revelation, "Babylon the Great, the mother of harlots and abominations of the earth" (Revelation 17:5), shall fall. An angel will proclaim the fall of Babylon: "Babylon is fallen, that great city, because she made all nations drink of the wine of the wrath of her fornication" (Revelation 14:8).
- Merrill F. Unger, Unger's Bible Dictionary, s.v. "Babylon," p. 116.
- Bible Encyclopedia, s.v. "Babylon," pp. 204-5.
- Bruce R. McConkie, Mormon Doctrine, Second Edition, "Babylon," p. 69.
- Our Original Heritage, The Story of Civilization, volume 1, p. 244.
- Ibid, pp. 205-6
- Old Testament Institute Manual, 1 Kings to Malachi, pp. 231-232.
- Learn more at MormonBible.org