20.2.3 time data which refers to decades and centuries
Very often we have expressions like the golden twenties, the twentieth century, the fashion of the fifties etc. etc. In English there is a special form of number for that, the cardinal numbers in plural. In Italian there are no special numbers for that, but in reference to decades the number stands behind (settant' anni = seventy years, gli anni settanta = the seventies).
gli anni settanta => the seventies
settant'anni => seventy years
In the case of decades the years get their names from the beginning (gli anni settanta = 20 to 29), in the case of century from the end (il diciannovesimo secolo = 1800 to 1899).
il ventesimo secolo = the twentieth century
il diciannovesimo secolo = the nineteenth century
Il ventesimo secolo era l' epoca della barbarie. = the tweentieth century was the era of barbarism
L' espressione i dorati anni venti è fuorviante. = The expression the Golden Twenties is misleading