Iron Sights
Mechanical sights with no magnification: front blade or post, rear notch or aperture. The original aiming system, still carried as backup behind an optic.
Modern military and precision rifles often mount iron sights as backups behind the primary optic. If the optic fails or fogs, the sights are still there. The classic NATO setup is a front post in a rear aperture (peep sight), which gives a fast, repeatable picture.
For precision distance work, a magnified optic gives you far more resolution and range than irons can. Their strong suit today is reliability backup, close-range fast shooting, or specific competition classes that mandate them.