 In circa 1250 BC, the first wave of destruction has been witnessed in various centers of mainland Greece for reasons that cannot be identified by archaeologists. These incidents appear to have triggered the massive strengthening and expansion of the fortifications in various sites. In some cases, arrangements were also made for the creation of subterranean passages which led to underground cisterns. Nevertheless, none of these measures appear to have prevented the final destruction of the Mycenaean palace centers in the 12th century BC. The reasons that lead to the collapse of the Mycenaean culture have been hotly debated among scholars. The two most common theories are population movement and internal conflict.
