劍橋詞典

abbreviation for Before Christ : used in the Christian calendar when referring to a year before Jesus Christ was born
公元前（Before Christ的縮寫）
The Battle of Actium took place in 31 BC. 阿尅提爾姆戰(zhàn)爭爆發(fā)於公元前31年。
比較
AD adverb (CALENDAR)
BCE 返回 BC