Mithraeum Ill at Nida was discovered in 1887. During private excavations undertaken at the site without authorisation in 1890, there came to light an iron key with a bronze handle. Purchased by the magistrate Ernst Justus Haeberlin, it remained in his private collection until the city of Frankfurt acquired it in 1940. This key has a square shank and a toothed blade at a right angle. Its termination is in the form of a protome of a lion emerging from a sort of floral calyx. The lion's head is damaged. This type was quite widespread and not specifically Mithraic.