expression, auxiliary verb
was; wasn't it?; is said to have ...
Archaic auxiliary verb used in classical Japanese to express personal recollection or hearsay, often with a nostalgic or narrative tone. Equivalent to modern 〜たそうだ or 〜たということだ.
昔、ここは大きな森なりけり。
Long ago, this place is said to have been a large forest.
「なりけり」は、古い物語でよく見られる言い回しです。
"Narikeri" is a phrase often seen in old tales.