The ruins of the Mycenaean acropolis at Glas are located to the north east of Copais. It was built in the Mycenaean era and was fortified with strong cyclopean walls, which had four gates. The wall was made of large stone blocks. There were only a few buildings in the interior, concentrated in a central enclosure. It is believed that it was under the control of Orchomenos and was the control and maintenance centre for the drainage works at Copais, as well as being the grain store for the area.
The acropolis at Glas is the largest fortified Mycenaean acropolis to survive within Greek territory. From the time it was constructed, its was neither supplemented or altered. The central building at Glas is the megaron. It conists of two wings and covered most of the area of the acropolis. The megaron had to entrances, and there were small separate buildings inside. Around the acropolis there were ditches to contain the water from the seasonal streams. The buildings at Glas were destroyed by fire, close to 1200 BC, and it was never re-occupied.