As historian James Neal Primm tells the story in Lion of the Valley, the two men had frequently squared off in the courtroom. Benton finally threw down the gauntlet after an argument during a trial, but Lucas demurred, saying he didn't want to be held personally responsible for things said in a court case. But passions flared again a few weeks later, and this time it was Lucas who challenged Benton.
The two men, each armed with a pistol, faced one another at the agreed-upon distance of 30 feet. Lucas' shot grazed Benton's knee. Benton's ball pierced Lucas through the throat. Both men survived.
Evidently the mutual wounding did not dissolve the animosity. Several weeks later Lucas and Benton met again on the island, pistols in hand. This time they paced off a mere ten feet. Benton shot Lucas through the heart and killed him.
Though the event marred Benton's reputation for a time, he was elected to the U.S. Senate in 1821 and went on to achieve fame and distinction as an orator and staunch proponent of Manifest Destiny.
The duelling ground, which came to be known as "Bloody Island," was the site of many a lethal confrontation during the nineteenth century. Eventually, the waters of the Mississippi washed it away.