From Roma Termini train to Rome airport, fly to Belgrade airport, then bus to Belgrade. 4hrs 55min 77 €. From Roma Termini train to Venezia Mestre, train to Tarvisio Boscoverde, train to Villach Hbf, then train to Beograd. 19hrs 08min 194 €. From Ara Coeli- Piazza Venezia line 492 bus to Rome, bus to Florence, then bus to Belgrade. 22hrs 33min 102 €. From Ara Coeli- Piazza Venezia bus to Roma, bus to Zagreb, then bus to Belgrade. 24hrs 43min 126 €. From Rome drive to Belgrade. 13hrs 17min 241 €.