The Prefecture of Serres covers an area of 3.790 square kilometers, from which 48% is characterized as lowlands, 3,4 % semi-mountainous and 18% mountainous . It is surrounded by mountain chains that define the limits of the Prefecture and provide natural protection, leaving two passages, one to the north through the Rupel Pass and one to the south, where the river bed of the river Strymon lies.
Northeast of the prefecture there is the mount Orvilos with an altitude of 2.212 m. , the highest summit in the prefecture, the mountains of Vrontous with and altitude of 1849 m ., mount Menoikio with and altitude of 1963 m . and finally on the east extremity of the prefecture there is the mount Paggaio with an altitude of 1.956 m. Among these mountain groups extends the large valley of Serres with farmlands covering163000 hectares of land, from which 61500 are irrigated. The valley extends on the north-south axis, along the Strymon river for most of its part, while over a shorter length, it spans along a direction parallel to the Aggitis river.
Source : Geography of Greece, Dimitrakou