The lid is very similar to another lid made by the same manufacturer
GJS-500-7 also called GGG50 marks a strong and heat-resistant type of metal while GJS is a sign for Continuously Cast Spheroidal Graphite Iron - which describes a process in which the metal is continuously fed.
Translation of the text on the cover: ΒΙOΦΡΕ - Viofre ΣΤΕΓΑΝΟ - Waterproof