A megalith is a large stone used in the construction of a structure, often a monument. Their use dates back to the Neolithic period, but appears to have largely died out by the Bronze Age. They appear throughout the Mediterranean and Europe, and the earliest known structures are chiefly French. The most common structure type is a portal tomb; upright stones with a flat stone used as a roof, though stone circles are best known in popular culture.
There is no evidence whatsoever that they have any connection to “druids” so kindly take your crystals elsewhere.