Though most collectors take dates on coins for granted, dates on coins
did not come into wide-spread use in Europe until the 16th century.
Prior to that time most rulers thought it sufficient to put their name
on the coin, and maybe a mark for the mint or person who made it.
Oriental coins generally were not dated until the 19th or 20th century.
However some mints made minor differences in the style of the characters
on Cash coins, which allowed the coins to be dated to the exact year they
were made even though they did not carry a visible date. Today, although
most oriental coins are dated, they are not always dated with an AD date.
Both Japan and Taiwan date their coins by the number of years the emperor
or government has been in power. Thailand coins are dated using the
Buddhist Era, but the same date may be struck for many years.
In the Middle East dating of coins goes back to ancient times, though coins
were often dated by the years that the king was in power. After the
rise of Islam coins began to be dated based on the number of years since
Mohammed fled to Medina in 622AD (AH date). However because the Islamic
calendar is a lunar rather than a solar calendar, the year is about 3%
shorter. Numerous other calendars have been used in various areas.
A set of coins using different dating systems can form a fascinating collection.