This is the 3003rd most frequent Russian word.
древних
"Ancient" or "of the ancients."
The word 'древних' is used as an adjective in the genitive plural form, describing 'цивилизаций' (civilizations) and indicating their characteristic of being ancient.
Наследие древних цивилизаций изучается учеными.
The heritage of ancient civilizations is studied by scientists.
The word 'древних' is employed as an adjective in the genitive plural form, qualifying 'времён' (times) to indicate their attribute of being ancient.
В музее хранятся артефакты древних времён.
The museum holds artifacts from ancient times.
In this context, 'древних' acts as a plural substantive referring to people from ancient times, functioning as the genitive plural form.