The X Corps entered Seoul the morning of September 25. By mid-afternoon, U.S. Army forces crossed the Han River and captured Namsan peak. The 1st Marine Division began its assault at 7 a.m. The North Koreans had heavily fortified the city. Buildings were heavily defended by machine guns and snipers, and on Ma Po Boulevard, the main road through the city, the KPA had established a series of 8-foot-high barricades of burlap bags, typically filled with sand, dirt, or rice. Located about 200-300 yards apart, each major intersection of the city featured such a barricade, the approaches to which were laced with mines, and which were usually defended by a 45mm anti-tank gun and machine guns. Each had to be eliminated one at a time, and it took the Marines, on average, 45-60 minutes to clear each position.