This is the 17616th most frequent Russian word.
тысячелетнюю
"Тысячелетнюю" means "millennial" or "thousand-year" in English, relating to a period of a thousand years.
Here 'тысячелетнюю' characterizes the culture as having a time span of one thousand years or more.
Они обсуждали тысячелетнюю культуру древней цивилизации в своих исследованиях.
They discussed the millennial culture of the ancient civilization in their studies.
In this context, 'тысячелетнюю' modifies 'статую', indicating that the statue is aged one thousand years.
Мы видели тысячелетнюю статую в музее во время экскурсии.
We saw a millennial statue in the museum during the tour.
The word 'тысячелетнюю' refers to the attribute of the history being millennial, describing a long-standing legacy.