When the Greek army had entered Thessaloniki in the First Balkan War ahead of the Bulgarian 7th division by only a day, they were asked to allow a Bulgarian battalion to enter the city. Greece accepted in exchange for allowing a Greek unit to enter the city of Serres. The Bulgarian unit that entered Thessaloniki turned out to be an 18,000-strong division instead of the battalion, which caused concern among the Greeks, who viewed it as a Bulgarian attempt to establish a condominium over the city. In the event, due to the urgently needed reinforcements in the Thracian front, Bulgarian Headquarters was soon forced to remove its troops from the city (while the Greeks agreed by mutual treaty to remove their units based in Serres) and transport them to Dedeağaç (modern Alexandroupolis), but still it left behind a battalion that started fortifying its positions.