Last fall someone in an adult education class asked me what the notations "B.C.E." and "C.E." meant. "Whatever happened to B.C. and A.D.?" she asked. Good question.

Chronology, which is the technical term for our words and thoughts about time, is strictly a matter of social convention, and cultures have counted years according to different systems.

Some ancient Greeks dated years according to Olympiads, which were four years long and began in 776 B.C.E. The Hebrew calendar dates from the year 3761 B.C.E. and progresses according to a solar schedule as divided by lunar cycles. The Islamic calendar dates from 622 C.E., which was the year that the prophet Mohammed moved to Medina. Because it follows a lunar cycle, a year has only 354 days.

Among numerous methods, some ancient Romans used the Greek Olympiad system. Others used a system that dated years "A.U.C.," an abbreviation signifying "from the foundation of the city [of Rome]," or "in the year of the city [of Rome]," traditionally dated to 753 B.C.E.

From the primitive church through the medieval period, Christians often dated years according to the Roman model in which years were reckoned forward from the founding of Rome. Thus, for example, what we have traditionally called 1 A.D. early Christians would have called 754 A.U.C.

Because the various calendar systems of the ancient Mediterranean basin produced widely divergent ways to reckon dates, it was hard to say exactly when a given event happened. We know from the North African bishop, Augustine of Hippo (354-430), that in 387 C.E., Easter was celebrated on March 21 (Gaul), April 18 (Italy), and April 25 (Alexandria). Fixing the exact date of Easter, and giving a precise schedule of future dates for Easter, was a longstanding and controversial problem in the early church. Various systems were used to calculate the cyclical pattern for Easter?s date until 525. Then a monk named Dionysius Exiguus solved the problem by proposing the system that we still use today.

He also argued that Christians ought to reckon years forward from the birth of Jesus Christ, although he himself continued to use a different, ancient way of dating years, which was according to the "indiction" (originally a 15- year tax cycle, in the medieval period dated from 312, the reign of Constantine). It was the Anglo-Saxon historian and theologian Bede (672-735) who first popularized the use of A.D. (anno domini—"in the year of the Lord"). Its use spread slowly throughout Europe, gaining prominence by the 11th century, except for Spain, where it took another 300 years to become common. But where did C.E. come from? And why has it replaced A.D.?

The use of C.E.—signifying "Common Era"—can be found at least 100 years ago, but it has become popular in recent decades. As Christians and others have become increasing aware that Christianity is not the only Western tradition, it has made sense to many to switch the designation of dates from A.D. to C.E., and thus also from B.C. ("Before Christ") to B.C.E. ("Before the Common Era").

Does this mean that we are no longer Christian when we use the terms B.C.E. and C.E.? Not at all.

For Christians, it is still Jesus Christ through whom God comes to us with healing redemption. It merely means that we ought not force this confession on others, if even implicitly.

So, Happy New Year—in 2003 C.E.

The Rev. John W. Riggs is Associate Professor of Historical Theology and Church History at Eden Theological Seminary in St. Louis, Mo.