Explain centuries during BC

In BC, time is counted backwards.

It counts back time before the Birth of Christ.

So if we can imagine the last day of the year turning into the next year, instead of adding a 1 to get the 'number' of the new year, we subtract a 1.

So if we look at the end of the year 20 BC.... it is New Year's Eve... tomorrow will be January 1, 19 BC.

Because of this the first century BC started on January 1, 100 BC and ended on December 31, 1 BC. (The next day would be January1, 1 AD).

The second and earlier centuries would have run as follows.... each going further back in time

2nd Century January 1, 200 - December 31, 101

3rd Century January 1, 300 - December 31, 201

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10th Century January 1 1000 - December 31, 901

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25th Century January 1 2500 - December 31, 2401.

If a building was erected in 1250 BC and stood for 8 centuries before being destroyed, then it would have collapsed in 450 BC.... in the fifth century Before Christ.