CHARLESTON, W.Va. -- The Battle of Fredericksburg, which took place 150 years ago, is best known for the bloody Union assault on Confederates dug in behind a stone wall at Mayre's Heights, overlooking the Rappahannock River town of 5,000.More than 8,000 federal troops were mowed down in Gen. Ambrose Burnside's unsuccessful attempt to wrest the high ground from troops commanded by Gen. Robert E. Lee in December of 1862. The defeat ended Burnside's career as commander of the Army of the Potomac after only 77 days, while strengthening Southern resolve to fight on.While the winter battle in a town only 60 miles north of the Confederate capital proved to be something of a hollow victory for the Southern cause, since it merely delayed the Union assault on Richmond until the following spring, it was historically significant for a number of reasons. Pulitzer-nominated author and historian Frank O'Reilly will discuss those reasons during a free public lecture beginning at 7 p.m. Thursday in the University of Charleston's Geary Student Union.Several actions that took place during the Fredericksburg campaign "anticipated 20th Century combat," O'Reilly said in a telephone interview from Virginia's Fredericksburg & Spottsylvania National Military Park, where he is park historian.One such action, he said, was the world's first amphibious landing under fire, followed by the first establishment of a beachhead in combat conditions."In 1862, no one had contemplated, studied, or drilled for such a thing," O'Reilly said. But the Union soldiers at Fredericksburg "made it up as they went along," he said, because if they were to have any chance of victory, "they had to defy conventional thinking and think outside the box."Burnside's plan for capturing Fredericksburg, and using it is a staging site for an assault on Richmond, depended on an un-resisted crossing of the Rappahannock, from which Confederate forces had removed all bridges in anticipation of a Union advance. The Union general ordered the components for several pontoon bridges to be brought to Fredericksburg to accommodate a speedy crossing before a force of Confederates could be assembled to block the attack. But the floating bridge parts arrived 10 days behind schedule, giving Lee's troops time to arrive on the Fredericksburg shore before they could be assembled.On Dec. 11, 1862, Union engineers began putting the bridges together. The span nearest downtown Fredericksburg was about halfway across the river when Confederates in a row of riverfront houses began firing on the assembly crew.Anxious to put an end to the sniping and complete their task, volunteers from the bridge-building crew piled into six of the clumsy, open pontoon boats, and after a barrage of Union artillery fire rained down on the Confederate riflemen, paddled toward the opposite shore."After they landed, they established a beachhead in a few of the riverfront homes," O'Reilly said. "That amphibious landing and the taking of a beachhead under heavy fire that followed became the great-grandaddy of similar actions at D-Day in World War II and Inchon during the Korean War."The 200 federal troops making the initial crossing soon became involved in another military first: the first urban combat to take place in North America. A brigade of Mississippians assigned to contest the Union crossing and delay the capture of Fredericksburg "fought house by house, block by block, in another 20th Century experiment," O'Reilly said. "At that time, military officers were trained to fight in open spaces, where they could maneuver easily and make use of en masse firepower from shoulder-to-shoulder formations of troops firing in volleys."But the development of rifling, or grooving the insides of gun barrels, made small arms fire more accurate and deadly, creating a role for snipers and small units of riflemen. Confederate leaders had hoped the Mississippians would be able to hold back the Union invaders for two or three hours; using a well-coordinated urban combat scheme that involved fortified fallback positions, they managed to delay the inevitable by more than 12 hours.While Fredericksburg proved to be one of Lee's easiest victories - one that led many historians to characterize Burnside as a well-meaning incompetent -- O'Reilly believes the Union Army commander's reputation may have been painted with too broad a brush."In truth, there's a lot to be said in favor of him," O'Reilly said. Unlike Maj. Gen. John McClelland, who he replaced, Burnside was "aggressive, assertive and driven. His plan to use Fredericksburg as a base from which to attack Richmond was a good one. His sudden arrival there caught the Confederates off guard."Had the pontoon bridges Burnside ordered arrived on time, allowing him to enter Fredericksburg before Lee's army arrived, "we may have been hailing Burnside as the greatest military commander of all time," O'Reilly said.O'Reilly's lecture, "From Stonewall to the Stone Wall: The Battle of Fredericksburg," is based on his book, "The Fredericksburg Campaign: Winter War on the Rappahannock," nominated for the 2003 Pulitzer Prize.The Battle of Fredericksburg "began changing American military strategy and ideas about how wars are fought," said Beth White, director of the 2012 Civil War Scholars Lecture Series, which is hosting the lecture, with financial assistance from the West Virginia Humanities Council and the University of Charleston.The outcome of the battle and the carnage it created "affected the mindset of military leaders both north and south," White said. She said O'Reilly's lecture would explore how that changed thinking influenced decisions by leaders of both sides and affected the remaining years of the war.The lecture series is a program of the Kanawha Valley Civil War Roundtable.Reach Rick Steelhammer at email@example.com or 304-348-5169.