Via Militaris or Via Diagonalis was an ancient Roman road, starting from Singidunum (today the Serbian capital Belgrade), passing by Danube coast to Viminacium (mod. Požarevac), through Naissus (mod. Niš), Serdica (mod. Sofia), Philippopolis (mod. Plovdiv), Adrianopolis (mod. Edirne in Turkish Thrace), and reaching Constantinople (mod. Istanbul). This road was connected with Via Egnatia by other roads - the road along river Axios (or Vardar), the Serdica–Thessalonica road along river Strymon (or Struma), and the road Philippopolis–Philippi.
It was built in the 1st century AD. The length from Singidunum to Constantinople was 924 kilometres.
During the first European conquests of Ottoman Turks orta kol (lit. middle arm) was following the Via Militaris.
In May 2010, while work was done on the Pan-European Corridor X in Serbia, well-preserved remains of the road were excavated in Dimitrovgrad, Serbia. The eight-metre wide road was constructed from large blocks of stone and had two lanes.