Snippet from Wikipedia: Siege

A siege (Latin: sedere, lit. 'to sit') is a military blockade of a city, or fortress, with the intent of conquering by attrition, or by well-prepared assault. Siege warfare (also called siegecraft or poliorcetics) is a form of constant, low-intensity conflict characterized by one party holding a strong, static, defensive position. Consequently, an opportunity for negotiation between combatants is common, as proximity and fluctuating advantage can encourage diplomacy.

A siege occurs when an attacker encounters a city or fortress that cannot be easily taken by a quick assault, and which refuses to surrender. Sieges involve surrounding the target to block provision of supplies and reinforcement or escape of troops (a tactic known as "investment"). This is typically coupled with attempts to reduce the fortifications by means of siege engines, artillery bombardment, mining (also known as sapping), or the use of deception or treachery to bypass defenses.

Failing a military outcome, sieges can often be decided by starvation, thirst, or disease, which can afflict either the attacker or defender. This form of siege, though, can take many months or even years, depending upon the size of the stores of food the fortified position holds. The attacking force can circumvallate the besieged place, which is to build a line of earth-works, consisting of a rampart and trench, surrounding it. During the process of circumvallation, the attacking force can be set upon by another force, an ally of the besieged place, due to the lengthy amount of time required to force it to capitulate.

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Snippet from Wikipedia: Battle of the Crater

The Battle of the Crater took place during the American Civil War, part of the Siege of Petersburg. It occurred on Saturday, July 30, 1864, between the Confederate Army of Northern Virginia, commanded by General Robert E. Lee, and the Union Army of the Potomac, commanded by Major General George G. Meade (under the direct supervision of the general-in-chief, Lieutenant General Ulysses S. Grant).

After weeks of preparation, on July 30 Union forces exploded a mine across from Union Major General Ambrose E. Burnside's IX Corps sector, blowing a gap in the Confederate defenses of Petersburg, Virginia. Instead of being a decisive advantage to the Union, this precipitated a rapid deterioration in the Union position. Unit after unit charged into and around the crater, where most of the soldiers milled in confusion in the bottom of the crater. Grant considered this failed assault as "the saddest affair I have witnessed in this war."

The Confederates quickly recovered, and launched several counterattacks led by Brigadier General William Mahone. The breach was sealed off, and the Union forces were repulsed with severe casualties, while Brigadier General Edward Ferrero's division of black soldiers was badly mauled. It may have been Grant's best chance to end the siege of Petersburg; instead, the soldiers settled in for another eight months of trench warfare.

Burnside was relieved of command for his role in the fiasco, and he was never returned to command, while Ferrero and General James H. Ledlie were observed behind the lines in a bunker, drinking liquor throughout the battle: Ledlie was criticized by a court of inquiry into his conduct that September, and in December he was effectively dismissed from the Army by Meade on orders from Grant, formally resigning his commission on January 23, 1865.

Background

During the Civil War, Petersburg, Virginia, was an important railhead, where four railroad lines from the south met before they continued to Richmond, Virginia, the capital of the Confederacy.

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