The deportation of 11,343 Jews (7,122 from Macedonia and 4,221 from Thrace) was organised and executed by the Bulgarian authorities, with the Treblinka extermination camp in Nazi-occupied Poland as their final destination. The Jews of Greek Thrace, Eastern Macedonia, and Pirot in Serbia, began to be rounded up 4 March 1943. They were transported by train via transit camps in Bulgaria to Lom on the Danube, then by boat to Vienna, and again by train to the death camp of Treblinka. The railway that carried the trains transporting Jewish deportees from Greece was constructed by Bulgarian Jewish forced labourers in the winter of late 1942 and early 1943. By 15 March, all but about a dozen of the Jews had been murdered at Treblinka. The Bulgarians had overestimated the number of Jews in the occupied territories and to fulfil the Belev-Dannecker pact, Belev drew up a plan to include approximately 8,000 Jews from within Bulgaria's pre-war borders, beginning in the southwest and in the capital.