The State Capitol building and its grounds have seen a lot of history since it was built almost 85 years ago.

But the history of the area is actually far older. An Indian mound by Capitol Lake, in what is now Arsenal Park, dates to about the year 1000, said Thurston Hahn, a historical archeologist with environmental consulting firm Coastal Environments Inc.

It’s the earliest known human structure in the capital area and was likely built by the same Native American tribes that used the “red stick” hunting marker that would later give the city its name.

Hahn told members of the Baton Rouge Genealogical and Historical Society on Saturday that the area had a vital role in shaping Baton Rouge’s history.

The Indian mound wasn’t the last time an artificial hill was built in the area, Hahn said.

“The State Capitol looks like it’s built on a hill. That’s not true. The hill was actually built around the Capitol,” he said.

He explained that when Gov. Huey Long decided to build his State Capitol, all the buildings on the grounds were cleared away and covered with a layer of sloping earth to create the new grounds. At that time, those buildings included military facilities and LSU’s campus, which was then moved to its current location.

The raised hill with a view of the river made the ground around the old Indian mound an attractive piece of real estate when European settlers did eventually arrive in the area, Hahn said. While French subjects were the first settlers in the early 1700s, it wasn’t until about 50 years later when English troops built an earth fort that Baton Rouge began as a successful colony.

That first fort, known by a number of names and controlled in turn by the English, Spanish, the short-lived West Florida Republic and the United States, has been the focus of much of Hahn’s research in the area.

Hahn displayed a series of hand-drawn maps from the 18th and 19th centuries he and his company used to establish the fort’s location. The maps showed the earliest illustrations of what would become Baton Rouge’s downtown area — Lafayette and Third streets stretched north into a path leading to the now-destroyed fort.

Hahn’s company is usually called in by the state when maintenance or construction work needs to be done at a location that may be archaeologically sensitive. This creates an opportunity to oversee the work while searching areas that may be otherwise inaccessible. In digs around the Capitol area, Hahn said his company has found a trove of artifacts, mostly military in origin — buttons, insignias, cannonballs, even a bugle.

He said no matter how much preparation he puts into a site, he can’t tell what the team will find until they start digging.

“We try to do as much research beforehand as we can. But sometimes we don’t have that luxury. Sometimes we get a call saying, ‘We need you out here next week,’ ” Hahn said. “I’ve seen sites where they’ve prepared, and they’re digging with heavy machinery and they don’t find anything.”

Hahn said Coastal Environments hasn’t had as many calls from the state in recent years, despite a number of construction projects around the Capitol.

The Pentagon Barracks, a group of four buildings on Third Street across from the Capitol, which are now primarily apartments for state legislators, were built by the U.S. Army in 1819, Hahn said.

Melanie Hanley, a new member of the Genealogical and Historical Society and formerly a board member for the Foundation for Historical Louisiana, said she was particularly worried about the lack of attention paid to the Pentagon Barracks and the lack of public access.

“Don’t you care if (the Barracks) has structural integrity?” Hanley asked. “I want to know. It’d be nice if they were doing some kind of studies. And it’d be nice if there was a tour once in a while.”