A series of fortified castles was constructed in the 14th century during the reign of king Kazimierz Wielki, who "When he ascended Poland was wooden, when he left us, it was from stone", as a system protecting trade routes and the borders of Malopolska. It consisted of many castles and strongholds picturesquely located on tall rock formations (hence the name - Eagle Nests). On the photo Olsztyn - one of the castles along the Eagles Nests Trail, built of local limestone.