Cain had relations with his wife and she conceived, and gave birth to Enoch; and he built a city, and called the name of the city Enoch, after the name of his son. (Genesis 4:17)The first city mentioned in Scripture was constructed by an unrepentant murderer. Cain named the city after his son, Enoch (note that this is not the Enoch in Genesis 5:24 who walked with God, also, for more information on Cain's wife click here).
Although Scripture says little concerning The City of Enoch, it is clear that the city was built on a godless foundation. The founder of the city was Cain himself! The City Of Enoch marked the beginning of man's foolish attempt to create a utopian society without God. It marked the expansion of the lineage of Cain, who was of the evil one (John 3:12). One can only wonder what role this city played in promoting all sorts of wickedness. Perhaps by the time of the great flood, the City of Enoch had grown to such a size (and such a level of wickedness) that it played a major role in God deciding to blot out almost all of humanity (see The Pre-Flood World Soon To Be Blotted Out).
The account of the construction of the City of Enoch is followed by a short genealogy:
Now to Enoch was born Irad, and Irad became the father of Mehujael, and Mehujael became the father of Methushael, and Methushael became the father of Lamech. Lamech took to himself two wives: the name of the one was Adah, and the name of the other, Zillah. (Genesis 4:18-19)Only a rough estimate (100 to 500 years) of the time which elapsed between the births of Cain and Lamech can be given. Nothing in the passage indicates whether the mentioned sons were firstborns. If they were all firstborns, it seems reasonable to assume that only 20 years passed between each of their births. However, it is also very possible that these sons were not all firstborns (for more information on this see When Was Seth Born?).
It seems this genealogy was likely included in order to establish a connection between Cain's evil actions and Lamech's evil actions. As Cain was the first recorded murderer in human history, so Lamech was the first recorded person to practice polygamy (Lamech, like Cain, was also a murderer).
Lamech's wives bore him three famous sons: Jabal, Jubal, and Tubal-cain. The accomplishments of each of these sons are discussed in Genesis 4:20-22.
The Cave Men of Genesis - Genesis 4
Who Was Cain's Wife? - Genesis 4:17
Age of the Earth - The Christian Worldview
What Does the Bible Say About Polygamy? - Genesis 4:19
Psalm 1:5 - Temporal Foundations