Keeping as true as possible to the time period has posed an interesting challenge in planning the mammoth event, which will include re-enactment of three battle scenarios, realistic military encampments and numerous historical demonstrations, organizers said.
That's on top of the incredible amount of logistical considerations inherent in planning any event of that scale - including devising a plan for getting tens of thousands of vehicles in, parked and out; setting up the site; and accommodating the needs of participants and spectators, they said.
"It's pretty mind-boggling when you think of all this," said Dennis Frye, president of the Association for the Preservation of Civil War Sites, the nonprofit group producing the event.
Frye said he expects between 10,000 and 12,000 military and civilian re-enactors to participate and up to 50,000 spectators to attend over the course of the weekend.
"We'll have the second-largest town in Washington County for three days, regardless of spectators," said Washington County Planning Director Robert C. Arch, chairman of the event's logistics committee.
The "town planning" component involved providing services - like security, communication, firewood, straw and water - for the thousands of re-enactors camping at the site and the sutlers, or Civil War-themed vendors, he said.
"To make it more difficult, the heart of this activity has to be done in a 19th century atmosphere," Arch said.
Some things - like the 200 portable toilets - were unavoidable. "We'll just try to make them as unobtrusive as possible," he said.
Other things, like power generation and the modern paved road through the property, were workable.
Larsen said he was able to find a silent generator to supply needed power during the event without making it sound like a carnival.
The generator will be concealed to keep up appearances, he said.
Starting Thursday, Rench Road will be covered with a mulch mixture from the county's rubble landfill "to appear much more like a highway of the day," Larsen said.
Historical accuracy had to be a constant thread throughout the planning process, which began in May 1996 with a handful of would-be organizers posing the concept to some area re-enactors, Frye said.
"There was great enthusiasm in the re-enactment community from the outset," he said.
Finding an appropriate site was the next major hurdle, Frye said.
Among the requirements were sufficient acreage; a terrain similar to the real battlefield; lack of modern "intrusions" like water towers, electrical lines or highways; appropriate spectator viewing areas; room for ample parking; and easy access, particularly to Interstate 81 and Interstate 70.
The Artz farm fit the bill.
Frye credits Washington County Commissioner John Shank for sharing his knowledge of the farming community and contacts in helping secure the property.
Once the site was secured, organizers had to decide - based on the site's features - which components of the Battle of Antietam would be re-enacted during the event.
For example, they couldn't re-enact the Burnside Bridge scenario because there isn't a stone bridge on the property, Larsen said.
They decided on three battle scenarios: A.P. Hill's Assault on Saturday and the Cornfield and "Bloody Lane" on Sunday.
A committee was formed to line up the hundreds of volunteers it will take for such things as parking control, ticket sales, information, commemorative program sales, and trash pickup, Larsen said.
For information on volunteering, call Jeff Driscoll at 301-665-1400.
Dealing with growing predictions on the event's turnout has kept organizers on their toes.
The event actually outgrew the Artz property, requiring organizers to secure adjacent Allegheny Power-owned farmland to the north for the federal encampment, Frye said.
Based on initial interest, Frye said had envisioned the event would draw 5,000 to 7,000 participants.
With more than 9,000 military and civilian re-enactors registered at this point, he said he now thinks it will be closer to 10,000 to 12,000.
"It's well on its way to being the largest re-enactment ever," Frye said.
To be on the safe side, preparations were made to accommodate up to 15,000 re-enactors, he said.