From Roma Termini train to Rome airport, fly to Belgrade airport, then bus to Belgrade. 4hrs 45min 79 €. From Roma Termini train to Venezia Mestre, train to Tarvisio Boscoverde, train to Villach Hbf, then train to Beograd. 19hrs 08min 187 €. From Ara Coeli- Piazza Venezia line 492 bus to Rome, bus to Siena, bus to Florence, then bus to Belgrade. 22hrs 44min 110 €. From Ara Coeli- Piazza Venezia bus to Roma, bus to Zagreb, then bus to Belgrade. 24hrs 43min 117 €. From Rome drive to Belgrade. 13hrs 17min 244 €.