According to legend, the island's origin is attributed to Zeus (Dia being the Greek name for Zeus). The myth recounts how Zeus, encountering a colossal sea monster threatening him near Crete, transformed it into stone with a mighty thunderbolt, thus giving rise to the island. During ancient times, Zeus held significance in maritime matters, particularly during the Minoan and Medieval periods when Dia was inhabited. Acting as a vital reference point for seafarers, the island also provided natural protection against northern winds, facilitating safe entry into the port.

Intriguing discoveries emerged from surveys conducted by the French oceanographer Jacques-Yves Cousteau in 1974-1975, utilizing a specialized submersible. In 1976, near the bay of Agios Georgios, Cousteau's team uncovered square and rectangular rocks forming an artificial breakwater on the seabed, known as the Cyclopean Walls. Cousteau proposed that this site might have been the largest and most significant port of Knossos.