The Jajce Mithraeum is a temple dedicated to the Persian invisible sun god, Mithra. It was rediscovered in an archaeological dig in 1931. The temple dates to the early 4th century AD, although it could be as ancient as the 2nd century AD with repairs undertaken during the early 4th century AD. This particular Mithraeum is one of the best preserved sites in Europe.
Mithra was worshipped throughout the Roman era, from the late Republic to the later Imperial era. The cult of Mithraism spread from the Middle East to other parts of the Roman Empire throughout the Mediterranean basin, at first by military-political adventurers, travelers, slaves and merchants from the Orient. Later, Mithraism was spread by soldiers whose legions came into contact with the followers of the cult in the East.
The Jajce site is a typical spelaea. Mithraism followers typically sought to set up their places of worship in caves. In absence of such topographical features, they excavated the soil and built small single-celled temple (spelaea) to reinforce the impression of a cave.
The temple is now protected by a modern steel-and-girder cage with glass walls that allows visitors to see inside without entering. Visitors can enter with advance notice by contacting the Ethnological Museum of Jajce.
The Jajce Mithraeum is declared a National Monument of Bosnia and Herzegovina, and, including the old Jajce walled city core, the waterfall and other individual sites outside of the old city perimeter, as part of wider areal designated as The natural and architectural ensemble of Jajce, proposed as a UNESCO World Heritage Site list.
References:The ancient Argos Theater was built in 320 BC. and is located in Argos, Greece against Larissa Hill. Nearby from this site is Agora, Roman Odeon, and the Baths of Argos. The theater is one of the largest architectural developments in Greece and was renovated in ca 120 AD.
The Hellenistic theater at Argos is cut into the hillside of the Larisa, with 90 steps up a steep incline, forming a narrow rectilinear cavea. Among the largest theaters in Greece, it held about 20,000 spectators and is divided by two landings into three horizontal sections. Staircases further divide the cavea into four cunei, corresponding to the tribes of Argos A high wall was erected to prevent unauthorized access into the theatron and may have helped the acoustics, but it is said the sound quality is still very good today.
Around 120 CE, both theaters were renovated in the Roman style.