In　this　paper,　the　structural　optimization　process　aiming　to　reduce　the　weight　of　the　superstructure　of　a　five　span　arch　bridge,　built　in　the　Province　of　Venice,　Italy,　and　spanning　the　Piave　River　in　the　town　of　San　Dona,　is　presented.　The　original　project,　with　a　pre-stressed　concrete　superstructure,　was　re-considered　during　construction　because　of　the　following　two　unexpected　events.　First,　the　approved　new　seismic　national　regulation　became　effective　when　the　bridge　was　already　partially　built.　As　a　result,　existing　foundations　became　unable　to　withstand　the　prescribed　new　seismic　action.　Furthermore,　the　Venice　Water　Authority,　responsible　for　the　management　of　the　river　spanned　by　the　bridge,　declared　that　erection　phases　without　any　provisional　supports　and　scaffolding　resting　on　the　riverbed,　as　foreseen　by　the　original　project,　should　be　preferred.　Between　the　two　possible　identified　design　strategies　able　to　deal　with　the　mentioned　problems,　namely,　the　strengthening　of　the　foundations　or　the　lightening　of　the　superstructure,　the　second　option　was　chosen,　on　the　basis　of　engineering　judgement　concerning　the　simplification　of　construction　procedures,　timing　and　budget.　The　search　for　the　lightest　possible　solution,　with　the　restraint　given　by　the　approved　aesthetics　of　the　original　design　and　the　need　of　keeping　within　the　former　budget,　brought　to　the　conclusion　that　an　evolutionary　structural　optimization　(ESO)　process　could　be　suitably　applied　to　a　composite　steel　and　concrete　superstructure.