one hundred years ago; a hundred years previously
A straightforward temporal expression indicating a point in time one century before the reference time.
百年前の今日、この建物が完成した。
One hundred years ago today, this building was completed.
百年前には想像もできなかった技術だ。
It's technology that couldn't have been imagined a hundred years ago.
Compound of 百 (hyaku, 'hundred'), 年 (nen, 'year'), and 前 (mae, 'before').