The 1st millennium BC, also known as the last millennium BC, was the period of time lasting from the years 1000 BC to 1 BC (10th to 1st centuries BC; in astronomy: JD 1 356 182.5 – 1 721 425.5). It encompasses the Iron Age in the Old World and sees the transition from the Ancient Near East to classical antiquity .
The first millennium of the anno Domini or Common Era was a millennium spanning the years 1 to 1000 (1st to 10th centuries; in astronomy: JD 1 721 425.5 – 2 086 667.5).The world population rose more slowly than during the preceding millennium, from about 200 million in the year AD 1 to about 300 million in the year 1000.