Most of the world measures time by saying
that something happened either before or
after the birth of Christ.
To do this, they use the words BC (Before
AD (Anno Domini-which means in the year
of the Lord)
Decades (10 years) are used to explain if
something happened tens of years ago.
Centuries (100 years). The first century was
began in the year 1AD.
Millennium (1000) years) is used to
describe something that happened over a
thousand years ago
https://muinteoirnimhurchu.files.wordpress.com/2014/08/how-historians-measure-time.pdf hope this helps.
one of the main ways historians measure time is with a time line. The other two ways are B.C. (Before Christ) and A.D. (Anno Domini)
they use B.C. (Before Christ), A.D. (Anno Domini AKA the year of the Lord), decades (10yrs), centuries (100yrs), millennium (1000yrs)