1At that time; in those days — referring to the particular time or period when an event took place, as viewed from the present.
当時はまだスマホが普及していなかった。
At that time, smartphones had not yet become widespread.
彼は当時、大学生だった。
He was a university student at that time.
当時の新聞記事を図書館で調べた。
I looked up newspaper articles from that period at the library.
当時は今ほど物価が高くなかった。
Prices weren't as high back then as they are now.