0s BC — the decade immediately before AD 1

The 0s BC refers informally to the final decade of the pre-AD era. The term is ambiguous because the traditional BC/AD system has no year zero; its use involves calendar conventions and historical context.

Overview

The phrase "0s BC" is used informally to indicate the decade leading up to the start of the Anno Domini era. In the conventional BC/AD (BCE/CE) numbering there is no year zero: 1 BC is immediately followed by AD 1. Because of that absence the label "0s BC" is ambiguous and appears chiefly in popular or casual discussion rather than in strict chronological scholarship.

Calendar and numbering issues

Under the traditional Christian era system the years run ... 3 BC, 2 BC, 1 BC, AD 1, AD 2 ... so a decade called the "0s BC" would typically be taken to mean 9 BC through 1 BC. Astronomical year numbering, used in some scientific contexts, does include a year zero (equivalent to 1 BC) and negative year numbers for earlier years; that system changes how "0s" labels map to calendar years. For more on conversion and conventions see calendar conversion and Anno Domini system.

Historical context

In the years before AD 1 the Mediterranean world was dominated by the Roman state under the rule of Augustus. Many regional events of political, architectural and administrative significance occurred in this period. In Judea, for example, the reign and death of Herod the Great are commonly placed in the years just before AD 1 (often cited around 4 BC), which is one reason why estimates of the birth date of Jesus of Nazareth fall earlier than AD 1 in much modern scholarship.

Characteristics and notable facts

The Julian calendar, introduced in 45 BC, was in general use across Roman territories during this decade.
Because the system lacks a year zero, arithmetic across the BC/AD boundary requires care (e.g., calculating intervals or decades).
Scholars sometimes use alternative year-numbering schemes for astronomy and chronology; consult early Roman Empire references for context.

In summary, "0s BC" is a convenient but imprecise label for the final decade before AD 1. Its meaning depends on whether one follows traditional historical notation or astronomical numbering conventions, and on the particular chronological questions being asked.