Historical Chronology Sources

“MEASURE OF TIME  

7 days = 1 week (wk.)  

365 days = 1 year (yr.)  

12 months (mo.) = 1 year 

[10 years = 1 decade] 

100 years = 1 century  

Years are numbered from the year of the birth of [Jesus] Christ. Those before his birth are marked B.C. ("Before Christ"). We say Rome was founded 752 B.C. 

Years since his birth are marked A.D. (Anno Domini [which means] "in the Year of our Lord")... 

Years are grouped in centuries. The first century of the Christian Era began with the year 1 A.D. and ended with the year 100 A.D. We live in the 20th century, the 19th [century] having ended with the year 1900, and the 20th having begun with the year 1901. It will end with the year 2000.  

Hence, the year-number ending in two [zeros] indicates the last year of the century.” 

Reference: 

Gleason, C. H., & Gilbert, C. B. (1912). The Gilbert Arithmetics, Book 2. New York: Macmillan, pp. 141–142.

Contextual statement: 

This book was a school textbook written over 100 years ago to teach students how to do maths. In one chapter, it explains how to count time and understand historical years like BC and AD. The authors, Charles Gleason and Charles Gilbert, were teachers who wanted to help students learn arithmetic in everyday life, including history and calendars. The book shows what school was like in the early 1900s.

“The terms ‘Common Era’ and ‘Before the Common Era’ are used by some writers instead of Anno Domini (A.D.) and Before Christ (B.C.). The [numbers] of the dates remain the same. Thus, 500 B.C. is the same as 500 B.C.E., and A.D. 500 is the same as 500 C.E.” 

Reference: 

Whitney, W. D. (Ed.). (1890). The Century Dictionary and Cyclopedia (Vol. 2, p. 1053). New York: The Century Co. 

Contextual statement:

This dictionary was made to explain the meanings of words and ideas to readers in the late 1800s. It was edited by William Dwight Whitney, a famous American language expert. At this time, people wanted detailed explanations of science, history, and religion in one big book. The entry on “Common Era” and “Before Common Era” helps explain different ways of writing historical dates without using Christian terms.