Tower of Babel
According to Genesis chapter 11, all humans spoke the same language immediately following the Great Flood of Noah. Those who settled in the land of Shinar built a city and a great tower out of baked bricks in order to make a name for themselves. [1]
And the whole earth was of one language, and of one speech. And it came to pass, as they journeyed from the east, that they found a plain in the land of Shinar; and they dwelt there. And they said one to another, Go to, let us make brick, and burn them thoroughly. And they had brick for stone, and slime had they for mortar. And they said, Go to, let us build us a city and a tower, whose top may reach unto heaven; and let us make us a name, lest we be scattered abroad upon the face of the whole earth. And the LORD came down to see the city and the tower, which the children of men built. And the LORD said, Behold, the people is one, and they have all one language; and this they begin to do: and now nothing will be restrained from them, which they have imagined to do. Go to, let us go down, and there confound their language, that they may not understand one another's speech. So the LORD scattered them abroad from thence upon the face of all the earth: and they left off to build the city. Therefore is the name of it called Babel; because the LORD did there confound the language of all the earth: and from thence did the LORD scatter them abroad upon the face of all the earth. Genesis 11, 1-9 (KJV) [2]
God cast down the Tower of Babel as an act of discipline, and scattered its builders as punishment for their lack of respect. God's intention is that mankind should be forever disunited, that human achievement shall be restricted, and that human ambition should never (again) rise to challenging Him.
Non-Biblical references
The Tower of Babel is mentioned in a number of other Apocryphal and Pseudepigraphical texts, notably the Ethiopian Book of Jubilees, and also in Rabbinic literature. A similar tale appears in the Koran, and a number of other cultures have similar myths.