The Point Douglas-St. Louis River Road Bridge near Stillwater was built in 1863 from locally quarried limestone rock. The bridge once carried part of the Point Douglas-Superior Military Road over Brown’s Creek. The 185-mile road was chartered by Congress to connect the Mississippi River with Lake Superior. The bridge is significant as the oldest extant bridge in the state, its association with transportation history and its masonry engineering. (The Minnesota Star Tribune)

It's just an inconspicuous gouge in a hillside along U.S. Hwy 10, easily overlooked by drivers whizzing to or from Prescott, Wis., across the nearby St. Croix River.

But it's one of the few remaining signs of Minnesota's first federally funded road project: the Point Douglas-Superior Military Road. Dating from the mid-1850s, the road formed an important link between the Mississippi River and Lake Superior, setting a route still largely followed today. And its construction was beset by the same kinds of challenges facing road projects more than 160 years later.

On July 18, 1850, when the area was still Minnesota Territory, Congress passed the Minnesota Road Act, authorizing and funding construction of five military roads. The roads would both ease troop movements for protecting the frontier and open up the area to land-hungry settlers.

The 185-mile roadway from the Mississippi where it met the St. Croix at Point Douglas — then a bustling settlement, now a ghost town — to the western point of Lake Superior was deemed a top priority. After several years of surveying and settling on a route, it was the first to be built, starting in 1855.

The route roughly followed today's Oakgreen Avenue in Washington County, then ran parallel to the St. Croix River before veering off in Chisago County to a roughly similar path along what would become Hwy. 61 and later, Interstate 35, before ending in Superior, Wis.

The road had its desired effect, drawing a flood of commercial traffic and easing transportation for early settlers, according to a history by the Minnesota Department of Transportation (MnDOT). When Minnesota became a state in 1858, responsibility for the road was shifted to the state, which — sound familiar? — did not have the funds to finish the project, then about two-thirds complete. Although very rough and in places incomplete, the road was still the best route north until railroads were built in 1870. Traces of the military road can still be seen in Wild River State Park and Banning State Park — and, in a very vivid way, in a tucked-away corner of Stillwater Township along Brown's Creek.

The Stone Bridge, built in 1863 (and lending its name to Stonebridge Trail, a road in Stillwater), was the crossing point over Brown's Creek for the Point Douglas-Superior Military Road. Before that, travelers apparently forded the creek over a bridge of fieldstone. The Washington County Board approved a $500 contract for two builders, Michael Hanley and Frederick Curtis, to build the bridge, a single-arched span of locally quarried limestone 20 feet long and 17 feet wide.

Sadly for the builders, when the county commissioners went to inspect the bridge before settling up, they determined the conditions in the contract had not been met, and refused to pay. Despite that, the bridge was used until 1891, when a larger bridge was built 200 feet to the east.

The bridge, according to MnDOT, is the oldest one standing in Minnesota, and remains a superb example of stone engineering — the opinion of that long-ago County Board notwithstanding. It was placed on the National Register of Historic Places in 1975.