Whwn we say 'nel cinquencento', we specifically mean the century from 1500 to 1599 (dopo Cristo). When we say 'nell'anno 500' indichiamo (in genere) l'anno 500 dopo Cristo, e se non vogliamo ambiguita` diciamo 'nell'anno 500 dopo Cristo'. Per indicare il periodo dal 500 al 599 in genere diciamo: - nel sesto secolo (il primo secolo arriva all'anno 99) oppure - nel sesto secolo dopo Cristo Mi sembra che il tuo libro in questo abbia ragione!

In Italian we say "nel Cinquecento" both to indicate "1500" (also written '500) and "500". As you can see, it can be rather ambiguous, so it is preferable to say "nel quindicesimo/sedicesimo/diciassettesimo( etc.) secolo". Expressions like "quindicento" don't exist. I hope this helped. Have a good day!

Usually we use "Cinquecento"/"Settecento"/"Novecento" to refer to the 1500s, 1700s and 1900s (even if it sounds like 500, 700 and 900). It is the most common use and it might sound a bit confusing, but if you clarify the context, people can easily understand if you are talking about the 6th century or the 16th century. In English there is a similar concept: it's like saying "the '50s", "the '70s" and "the '90s" to refer to 1950s, 1970s and 1990s. Of course these decades don't only exist in the 1900s, but it's the most common use.