The western-style year dating convention commonly used in many parts of the world was created by the monk Dionysius Exiguus in or about the year AD 532.
Later, all dates prior to Christ’s birth were identified as B. (= before Christ) and all dates after Christ’s birth were identified as A.
For instance, in the date AD 2001, the prefix "AD" stands for "Anno Domini" which is Latin for "the year of our Lord." Similarly, in the date 500 BC, the suffix "BC" stands for "Before Christ." In sixth century Europe, the concept of "zero" was still unknown. Furthermore, modern scholars believe Christ's birth was actually four years earlier than Exiguus thought.
In spite of these deficiencies, the dating system devised by Exiguus is now too deeply ensconced in the Western world to easily change.
Perhaps the most unfortunately characteristic of this convention is that "BC" is a suffix (used after the year) while "AD" is a prefix (used before the year).
This is inconvenient when generating computerized lists because extra columns must be reserved for both prefixes and suffixes.