A Brief History of AD BC

Commonly understood definitions are the cornerstone of effective marketing, particularly when it comes to measuring customer engagement and performance metrics. Without shared definitions, comparisons across campaigns, teams, or timeframes become meaningless, leading to confusion and inconsistent results. A clear and universal framework ensures that everyone—marketers, analysts, and stakeholders—interprets data in the same way, enabling accurate assessments of performance and the identification of actionable insights. Establishing these definitions is critical for aligning strategies, driving accountability, and ensuring the meaningful evaluation of success in marketing initiatives.

But sometimes, the history behind these definitions is forgotten. Take, for example, the way historians use AD and BC to define and organise time. These terms, which have shaped our understanding of historical chronology for centuries, originated with specific cultural and religious purposes that are often overlooked today. Exploring the story behind these definitions offers a fascinating glimpse into how shared systems of measurement can evolve—and how their origins can sometimes reveal as much as the metrics themselves.

The concept of counting years from the birth of Jesus Christ was first introduced in 525 CE by Dionysius Exiguus, a Christian monk. Dionysius aimed to create a Christian calendar that would be acceptable to both the Western and Eastern churches, primarily to stabilise the date of Easter. He sought to replace the Alexandrian system, which dated events from the beginning of the reign of the Roman emperor Diocletian, known for persecuting Christians. Dionysius intended his system to count years from the incarnation of Jesus; however, the exact date of Jesus' birth remains uncertain. It is widely believed that Jesus was actually born sometime between 6 BCE and 4 BCE, during the reign of King Herod.

The BC/AD dating system is inherently flawed, as it misrepresents the timing of Jesus' birth by approximately seven years. One reason for the absence of a year zero is the lack of a concept of zero at the time, even in the 6th century CE. Roman numerals, which were commonly used, do not include zero.

Dionysius’ system did not originally include the designation "AD." The term Anno Domini (in the year of the Lord) was popularized by the English monk Bede in 731 CE through his work The Ecclesiastical History of the English People. Bede experimented with expressions like "in the sixtieth year before the time of the Lord’s incarnation" to refer to years preceding the AD era. The Latin Anno Domini gained further prominence during the reign of Charlemagne (800–814 CE), who implemented the system to standardise dating across Europe. However, it wasn’t until the 15th century that the AD system was universally adopted in Europe.

The term "BC," on the other hand, emerged much later in a post-Reformation world, where vernacular languages became more prevalent. The phrase “in the year before the birth of Christ” was first used by the German monk Werner Rolevinck in 1474, while the Latin term ante Christum ("Before Christ") was popularized in 1627 by the French Jesuit theologian Denis Pétau.

Note: In recent years, there has been a move to replace the terms BC (Before Christ) and AD (Anno Domini) with BCE (Before Common Era) and CE (Common Era). This change reflects a more inclusive and secular approach to historical dating, as BCE and CE are not tied to religious connotations, making the system applicable across cultures and belief systems.