$30 million mansion in Maryland built before America existed.

The estate sits on 500 acres and borders the Potomac River. It's hard to believe that a house built before the country was founded is still standing, let alone for sale. But this is the truth about the formal estate, which is a cultural and architectural time capsule and was built in 1755 on land along the Potomac River in Maryland.

Mulberry Fields in Leonardtown

consists of more than just an estate. There are more than a dozen apartments, cottages, and barns (some historic, some added) on what was a thriving plantation in the 18th century. Along with the buildings, the estate sits on 500 acres of land, with a majestic avenue of cedar trees on the south side leading to a mile''white-sand beach on the river.

The manor house

Dating back to the 18th century, it remains an architectural time capsule. It and the property itself have remained in the hands of the current owners' family for more than a century. The price tag is $30 million.

Mulberry Fields is the only surviving Georgian-style house in "a neighborhood that once boasted several such structures," according to the National Register of Historic Places. The former plantation was added to the historic register in 1973.

A road lined with cedar trees with a wooden fence leads to various structures on the property. Outside, a tree-lined road leads to a house that has an Annapolis-style facade. But it's the entrance that draws the most attention''from the river on the south side: large central doors with two large windows on the sides (in former times one could arrive by boat). An elaborate two-story portico with long Doric columns was added around 1820.

Numerous wood paneling, moldings, and fireplaces have been preserved inside.

For example, walls of rectangular raised panels stretch to the ceiling in the living and dining rooms on the first floor.

Historic details include numerous wooden elements. There are three bedrooms on the second floor and three bedrooms on the third floor.

The home is surrounded by two separate period buildings: the kitchen, which was''Renovated as a guest cottage, and a weaver's cottage which retains its original wedge board walls, flooring, doors and fittings. Both have pitched roofs and brick facades. These "dependencies" or outbuildings were formerly inhabited by slaves who served as cooks, stable boys, servants and maids.

Many fireplaces used to be the only sources of heating.

The grounds also include a dairy farm, a smoke house, a stable, a garden and tool shed, several animal and equipment barns, one of which has been converted, as well as a farmhouse and an old dwelling.

It's not hard to imagine a modern lifestyle on this land, with bonfires on the beach by the river, walks in the fields and woods, and''organizing entertainment in the historic living room.

Paneled walls surround the dining room.

The house was built by John Attaway Clark and then passed into the possession of his nephew William Somerville, who had a labor pool of slaves working the fields to grow corn, wheat, flax and cotton in the early 1800s. Ownership eventually passed to his son William Clark Somerville, the house's most famous owner, who distinguished himself while serving as a U.S. military major during the War of 1812.

Somerville traveled to Europe and socialized with poet Lord Byron, the famous British Duke of Wellington and the Marquis de Lafayette, who fought in the War for American Independence as a young man. Later he''received a diplomatic assignment to Greece from then-President John Quincy Adams, but died on his way home to Lafayette.

The estate went through several hands before passing to the current owners, who have architectural plans and permits to remodel the kitchen and bathrooms and customize a new wing on the west side of the house.

The current lease on the property generates $70,000 in income. There is room for 12 rental apartments on the estate. Income also comes from agriculture and the U.S. Navy, which maintains a navigation signal on the river.

Two brick buildings next to the estate were used for cooking, weaving and housing slaves...

As for the buyers, the owners''s hope is that the property will go to someone who will protect this historic gem. "The owners and their families over the generations have been very active in preserving its history and not destroying it with renovations here and there," says sales agent Cornelia Stuphan of Long & Foster Real Estate. "We'd like to see it preserved. We're hoping for a historical organization or foundation." Whoever ends up buying Mulberry Fields will acquire a rare piece of American history.

Mulberry Fields is located at 19700 Mulberry Fields Road in Leonardtown, Maryland.