The present paper refers to the major part of the Egnatia highway, about 100 km long, which connects Thessaloniki and Kavala cities in North Greece. Actually, it is divided in three parts: i) Nymphopetra-Asprovalta, about 40 km long, ii) Asprovalta-Strymonas, about 20 km long and iii) Strymonas-St. Andreas, about 40 km long. The highway has already been constructed. Driving from the west to the east, the highway, at the beginning of Nymphopetra-Strymonas part, passes nearby Volvi lake, at the foot of Vertiscos Mountains. Easterly, it passes through Kerdillia Mountains, Strymona’s river and it leads to Pangeo’s mountain, ending through Symbol Mountains. The highway also passes through five tunnels; i) Vrasna tunnel, which is located at Nymphopetra – Asprovalta’s part, ii) Asprovalta’s tunnels, which are three tunnels locating at Asprovalta – Strymona’s part and iii) Symbol tunnel, which is located at the last Strymonas – st. Andrea’s part. The paper describes the support measures against geological failures during the construction of the highway. For this purpose, the mechanisms of sliding and rock falling procedures were studied. As far as slopes concern, the orientation of the discontinuities and the poor quality of the rock mass, that creates cyclic sliding, were responsible for the instabilities. Rainfall also helps landslides to be occurred. During the tunnelling excavation, the sliding along a plane, the décollement from the roof and the fall of wedges were the common failure causes.