expression, noun
page in history; historical event; old news
Used figuratively for a notable event that will be remembered, or for something already in the past. The 'old news' sense is often in negative or dismissive contexts.
この発見は歴史の１ページに刻まれるだろう。
This discovery will be recorded as a page in history.
そのスキャンダルはもう歴史の１ページだ。
That scandal is already old news.
A set phrase combining 歴史 (history) and １ページ (one page), literally 'one page of history'. The figurative use is straightforward.