 Romania declared war on Austria-Hungary on 27 August, and two days later it captured Brassó, which - at 41,000 inhabitants - was the second largest city in Transylvania, behind Kolozsvár, which had almost 63,000 inhabitants.German forces soon reinforced the Austro-Hungarians, and the two Central Powers began a counteroffensive in the region in late September.In early October, the Romanian 2nd Army succeeded in thwarting a Central Powers attack, but - instead of exploiting its victory offensively - the Romanians unexpectedly began to retreat, preventing the Central Powers from pinning them down.