Which Chinese dynasty built most of the existing Great Wall?

The Ming dynasty built most of the existing Great Wall.

The Ming dynasty ruled China from 1368 to 1644 and constructed or extensively rebuilt major wall sections, especially after conflicts with northern Mongol groups. Many familiar stone and brick watchtowers, battlements, and fortified passes date from this period.

The Great Wall is not one continuous structure built at one time. Earlier states and dynasties, including the Qin and Han, built separate defensive walls, and later rulers expanded, connected, or abandoned sections. The Ming government used walls as part of a broader frontier defense system that also included garrisons and signal towers.

The Qin dynasty is often associated with the first large-scale connection of earlier walls, but much of that early construction has not survived in the form seen by modern visitors. The best-preserved tourist sections are predominantly Ming-era.