The

**1st century BC**, also known as the last century**BC**, started on the first day of 100**BC**and ended on the last day of 1**BC**.The AD/**BC**notation does not use a year zero; however, astronomical year numbering does use a zero, as well as a minus sign, so "2**BC**" is equal to "year –1".Millennium: : 1st millennium

**BC**Centuries: : 2nd century**BC**1st century**BC**1st century; Decades: : 40s**BC****30s****BC**20s**BC**10s**BC**0s**BC**Years: : 23**BC**22**BC**21**BC****20 BC**19**BC**18**BC**