Allied troops who had recaptured the imperial capital of Hue from the North Vietnamese during the Tet Offensive discover the first mass graves in Hue. It was discovered that communist troops who had held the city for 25 days had massacred about 2,800 civilians whom they had identified as sympathizers with the government in Saigon. One authority estimated that communists might have killed as many as 5,700 people in Hue. The Tet Offensive had begun at dawn on the first day of the Tet holiday truce (January 30), when Viet Cong forces, supported by large numbers of North Vietnamese troops, launched the largest and best coordinated offensive of the war. During the attack, they drove into the center of South Vietnam’s seven largest cities and attacked 30 provincial capitals ranging from the Delta to the DMZ. Among the cities taken during the first four days of the offensive were Hue, Dalat, Kontum, and Quang Tri; in the north, all five provincial capitals were overrun. At the same time, enemy forces shelled numerous allied airfields and bases. By February 10, the offensive was largely crushed, but resulted in heavy casualties on both sides.