How many millennia are shown on the time line 2001 B.C. through 2001 A.D.?

The timeline from 2001 B.C. to 2001 A.D. spans a total of four millennia. This includes the first millennium B.C. (from 3000 B.C. to 2001 B.C.), the second millennium B.C. (from 2000 B.C. to 1001 B.C.), the first millennium A.D. (from 1 A.D. to 1000 A.D.), and the second millennium A.D. (from 1001 A.D. to 2001 A.D.). Thus, the timeline covers a total of 2001 years, which includes four distinct millennia.