Many people find it difficult to answer the question: "How to determine the century by the year in which this or that event occurred?" In general, there is nothing complicated. Now you will see it yourself.
our era
For events that occurred in the time period of our era (i.e., everything that was from our days to a period of just over two thousand years ago), the century is calculated as follows: the last two digits are discarded from the year, and one is added to the result. Suppose we need to find out in what century the Great Patriotic War began. This happened in 1941. We discard the last two digits (41) and add one to the remaining digits (19). It turns out the number 20. That is, The Great Patriotic War began in the twentieth century. Another example - Prophetic Oleg died in 912. What century was it? We discard the numbers 12, add one to the nine and understand that the Kiev prince died in the tenth century.
Here you need to make one clarification. A century is a span of one hundred years. If the last two digits of the year are 01, then this is the first year of the beginning of the century. If 00 is the last year of the century. Thus, there is an exception in our rule. If the last two digits of the year are zeros, then we do not add one. How to determine such a century by year? For example, Pius VII became Pope in 1800. In what century did this happen? We discard the last two digits of the date, but keep in mind that these are zeros, and do not add anything. We receive 18. Pius VII became the Pope in the XVIII century. And as early as next year, the nineteenth century came. We figured out the definition of which century which year includes, relative to our era. And if we are talking about events that happened earlier?
BC
Everything is a bit more complicated here. From 1 year to 100 BC - this is the first century BC From 101 to 200 - the second, and so on. Thus, to determine the century by the year before the birth of Christ, it is necessary to discard the last two digits of the year and add one. And in the same way, with the last digits of two zeros - we do not add anything. Example: Carthage destroyed in 146 BC e. How to determine the century by year in this case? We discard the last two digits (46) and add one. We get the second century BC And let's not forget about our exception: the catapults were invented in 400 BC. We drop the last two digits, keep in mind that these are zeros, and do not add anything. It turns out that catapults were invented in the 4th century BC. Everything is simple!
Millennium
Since we figured out how to determine the century by year, let's try at the same time to learn how to determine the millennium. There is also nothing complicated. Only it will be necessary to discard not the two, but the last three digits of the date, but add 1 as before.
Example: Alexander II abolished serfdom in 1861. In what millennium did he do this? We discard the last three digits (861) and add one more to the remaining unit. Answer: the second millennium. There are exceptions here too. If the last three digits are zeros, then the unit is not added.
The national currency "somoni" was introduced in Tajikistan in 2000. That is, this happened in the second millennium.
That is why those who in 2000 celebrated the onset of the third millennium and the 21st century were mistaken - these events occurred only the next year.
If you understand all this simple arithmetic, now you know exactly how to determine the century by year or even find out the number of the millennium.