Posted by John Keller .

U.S. Army Maj. Robert Anderson had passed a troubled night with little, if any, sleep, as he gazed with dread over the parapets of Fort Sumter across the still-dark harbor waters of Charleston, S.C. It was just before 4:30 a.m., 12 April 1861, and the big guns along the waterfront had never looked so menacing.

The standoff had gone on for months, but this morning it was different. The previous December the state of South Carolina, just where he and his small garrison found themselves this day, had voted to leave the Union, and no longer considered themselves part of the United States -- the country for which Maj. Anderson wore his blue uniform.

Anderson and his garrison had occupied Fort Sumter in the middle of Charleston Harbor at about the same time South Carolina seceded, and Anderson, commanding officer at the fort, had refused all demands by the new South Carolina government to surrender this edifice guarding the harbor entrances.

Anderson and his president, Abraham Lincoln, still considered Fort Sumter to be U.S. government property, but South Carolina officials believed the fort to be theirs, and they flatly told Anderson that further attempts to hold it would lead to war.

It happened at 4:30 a.m., 150 years ago this morning. Anderson heard the first cannon fire, saw the twinkling fuse of the shell as it rose upward, pausing a moment at the top of its trajectory, and plunge toward him and Fort Sumter.

It was the first shot of the American Civil War, which over the next four years would claim more than 600,000 casualties -- nearly 2 percent of the nation's entire population -- and seared into the national memory place names like Bull Run, Antietam Creek, Fredericksburg, Chancellorsville, Gettysburg, and the Wilderness.

Maj. Anderson, however, didn't know any of that yet. All he knew was his fort was the target of a ring of fire around Charleston Harbor. He was outgunned, low on supplies, and had no chance of relief. He held on for two grim days before lowering his flag and surrendering.

Before he left Fort Sumter on 14 April, however, Maj. Anderson took the fort's flag. He went with it to New York City where he showed it off at a Union Square rally that was largest public gatherings that New Yorkers had seen up until that time.

Anderson was promoted to brigadier general, but he had seen his worst fighting of the Civil War. He went to Kentucky to help enforce that state's neutrality in the Civil War, but had to turn over command due to worsening health. Replacing Anderson was another brigadier general named William T. Sherman.

Anderson formally retired from the U.S. Army two years later due to declining health. At war's end in 1865, however, he returned to Fort Sumter, wearing his uniform and bearing the flag he had lowered on that April morning.

He raised that flag once again over the now-crumbling fortress.