By noon of May 18, with Grant’s advance expected momentarily, Pemberton believed the defenses of Vicksburg strong enough to stand off the Union Army until Johnston received sufficient reinforcements to raise the expected siege and prevent loss of the Mississippi River. There, while inspecting his defenses, Pemberton received a dispatch from Johnston advising the evacuation of Vicksburg which, Johnston felt, was already doomed. Military necessity demanded that “instead of losing both troops and place, we must, if possible, save the troops. If it is not too late, evacuate Vicksburg and its dependencies and march to the northeast.” Unwilling to yield the city without a fight, Pemberton placed the order before his senior officers. They were of unanimous opinion that it would be “impossible to withdraw the army from this position with such _morale_ as to be of further service to the Confederacy.” As the council of war reached its decision to remain and fight, Union guns opened on the works. The siege of Vicksburg had begun. _The Siege of Vicksburg_ THE CONFEDERATE DEFENSE LINE. From his assumption of command 7 months before, Pemberton had put his engineers to work constructing a fortified line which would protect Vicksburg against an attack from the rear. A strong line of works had been thrown up along the crest of a ridge which was fronted by a deep ravine. The defense line began on the river 2 miles above Vicksburg and curved for 9 miles along the ridge to the river below, thus enclosing the city within its arc. So long as this line could be held, the river batteries denied to the North control of the Mississippi River. At salient and commanding points along the line, artillery positions and forts (lunettes, redans, and redoubts) had been constructed. The earth walls of the forts were up to 20 feet thick. In front of these was dug a deep, wide ditch so that assaulting troops which climbed the steep ridge slope and reached the ditch would still have a high vertical wall to climb in order to gain entrance into the fort. Between the strong points, which were located every few hundred yards, was constructed a line of rifle pits and entrenchments, for the most part protected by parapets and ditches. Where spurs jutted out from the main ridge, advanced batteries were constructed which provided a deadly crossfire against attacking lines. The Confederates had mounted 128 artillery pieces in these works, of which 36 were heavy siege guns; the remainder, field pieces.