Oh . . . about 6000 years ago.
1 century = 100 years The 25th Century BC includes all the years from 2500 BC to 2401 BC. Right now, as we write this, the year is 2011. The 25th Century BC was the period from 4,511 years ago to 4,412 years ago.
3000 BC has already happened and it can't happen again because its AD now. For it to be 3000 AD it'll be 989 years.
2451 years
470 years.
49 years
545 years.
208 years
2451 years.
918 years
2451 years
2450 years