Most wine bottles are indented at the bottom (which is called a punt), and there are several reasons for that. Historically, a punt is a remnant of the old technology of blowing glass. The bottles were produced in this way because a dent on the bottom creates a stable surface for the bottle. Today, the bottles are produced mechanically and are much stronger, so indentation on the bottom is only part of the wine tradition. A punt is no longer so important for the structural stability of the wine bottle, except for champagne and sparkling wines bottles, which are under pressure. In these cases, the indentation make the bottom of the bottle stronger and thus ensures that the bottle will endure the pressure.
In addition to stability, a punt also allows the sediment from wine to deposite in the "ring" at the bottom of the bottle and in that way to prevent its return back to the wine when it is poured into a glass. A punt also facilitates holding the bottle in one hand, because the thumb can be placed in the middle of the recess, while the other fingers sticking to the outside of the bottle. The size of the punt is not an indicator of quality or category of wines, but indentation makes the bottle appear larger, creating the impression that the bottle contains more wine than it really does.