On 12 October 1999, the Russian forces crossed the Terek and began a two-pronged advance on the capital Grozny to the south. Hoping to avoid the significant casualties that plagued the first Chechen War, the Russians advanced slowly and in force, making extensive use of artillery and air power in an attempt to soften Chechen defences. Many thousands of civilians fled the Russian advance, leaving Chechnya for neighbouring Russian republics. Their numbers were later estimated to reach 200,000 to 350,000, out of the approximately 800,000 residents of the Chechen Republic. The Russians appeared to be taking no chances with the Chechen population in its rear areas, setting up "filtration camps" in October in northern Chechnya for detaining suspected members of "bandformirovaniya" militant formations (literally: "bandit formations").