Created in 1956, the Roundtable meets once a month for eight months a year, and makes a point of emphasizing the everyday people, such as Brendel, who made sacrifices during the Civil War.
It's not a group of stuffy academics sitting around a table and discussing highbrow topics, Mayhue said.
"This isn't just for intellectual Civil War enthusiasts. This is for everybody that has an interest in the Civil War," Mayhue said. "In other words, we don't talk over your heads. If you just have a general interest in the Civil War, you're welcome."
Membership in the organization is open to anyone 14 years old and older. Dues include a one-time $10 fee and an annual fee of $20. A subscription to the group's newsletter, The Bugle Call, is included with the membership.
Most meetings, held at the Four Points Sheraton on Dual Highway in Hagerstown, are preceded by a catered dinner.
The Roundtable's purpose is to promote and stimulate interest in all aspects of the Civil War era, Mayhue said.
A wide range of topics is discussed during the meetings.
"About anything you can think of, we've had a topic of in regards to Civil War history," Mayhue said.
Several of the group's members or speakers have included authors, including John Schildt, Joe Harsh, Dennis Frye and Roger Keller.
The Roundtable has about 100 members, and typically 40 to 50 show up for meetings, which are held from September to May.
Mayhue, a Hagerstown firefighter, said his interest in the Civil War was piqued when his father took him to several battlefields, including Antietam, Gettysburg, Pa., and Shiloh, Tenn.
That interest deepened when Mayhue learned during a genealogy search that some of his ancestors fought for the Union in the war. One of those ancestors was a great-great-grandfather who was captured and held as a prisoner of war at Harpers Ferry, W.Va.
During local filming of the movie "Gods and Generals," Mayhue was part of a "core company" of extras who portrayed both Union and Confederate soldiers. He said he can be seen in several scenes of the film.
After a friend who was aware of Mayhue's interest in the Civil War presented him with Brendel's 144 letters, Mayhue said he read them with interest, and plans to compile them into a book.
Brendel, a member of the 11th Pennsylvania volunteer infantry unit, was from West Newton, Pa., and fought in several major battles.
As well as hosting speakers, the Roundtable awards an annual scholarship to a student interested in history, has a foundation with a goal of awarding additional scholarships and presents an award to an individual who has excelled in preserving local Civil War history.
It makes donations earmarked for Civil War land preservation, and members go on a bus trip to a Civil War site about once a year, Mayhue said.