The Nebra sky disk is a bronze disk of around 30 cm diameter and a weight of 2.2 kg, with a blue-green patina and inlaid with gold symbols. These are interpreted generally as a sun or full moon, a lunar crescent, and stars (including a cluster interpreted as the Pleiades).
The disk is attributed to a site near Nebra, Saxony-Anhalt in Germany, and associatively dated to c. 1600 BC. It has been associated with the Bronze Age Unetice culture.
The disk is unlike any known artistic style from the period, and had initially been suspected of being a forgery, but is now widely accepted as authentic.
Check out the Wikipedia page for the breakdown on how they think the disk evolved over time and had its various components added onto it, as well as the weird story of how it was found, suspected of being a forgery, and finally vindicated as authentic.