 At 03 : 40 on the foggy morning of 31 January , allied defensive positions north of the Perfume River in the city of Huế were mortared and rocketed and then attacked by two battalions of the 6th PAVN Regiment . Their target was the ARVN 1st Division headquarters located in the Citadel , a three @-@ square mile complex of palaces , parks , and residences , which were surrounded by a moat and a massive earth and masonry fortress built at the beginning of the 19th century by Emperor Gia Long . The undermanned ARVN defenders , led by General Ngô Quang Trưởng , managed to hold their position , but the majority of the Citadel fell to the PAVN . On the south bank of the river , the 4th PAVN Regiment attempted to seize the local MACV headquarters , but was held at bay by a makeshift force of approximately 200 Americans . The rest of the city was overrun by PAVN forces which initially totaled approximately 7 @,@ 500 men . Both sides then rushed to reinforce and resupply their forces . Lasting 25 days , the battle of Huế became one of the longest and bloodiest single battles of the Vietnam War . 
