ATHENS, Greece (AP) — Excavations next to the uninhabited Greek islet of Keros, already identified as the enigmatic hub of a forgotten religion, have now revealed traces of intense industrial activity more than 4,500 years ago, Greece's Culture Ministry said Wednesday.

Digs last summer showed that Dhaskalio, a rocky islet once joined to Keros, was once almost completely covered in unique monumental structures of gleaming white marble. It also had metal-working facilities and houses, with a sophisticated drainage system underneath.

According to a ministry statement, Keros, between the bigger is...