The name of King Samsu-iluna’s 24th year

How do we know what year it is? Nowadays we most often use the birth year of Christ as the anchor for counting years. But there are many other ways of keeping track of the years: the Muslim calendar for example uses as its starting point the Hijrah (migration) of Mohammad from Mekka to Medina, and the Jewish calendar uses as its starting point the creation of the world according to the Bible some 5782 years ago. But how else did people in Antiquity know what year it was? For example in ancient Mesopotamia, one of the oldest known civilizations? This object tells us how people knew what the current year was in 1725 BCE.