When the British burned the White House and the Capitol in the War of 1812, the country responded by buttressing its shores against another foreign invasion, building coastal forts from New England to New Orleans to ward off invaders.

Two centuries later, some of the oldest examples of that line of fortification are washing away as Louisiana's coastline erodes at a rate of about 25 square miles a year -- an area the size of Delaware lost since the 1930s.

State officials are trying to find ways to preserve places such as crumbling Fort Livingston, which was built to protect New Orleans from an attack via Barataria Bay.

Martello Castle, built closer to the city, was once on solid ground but is now surrounded by Lake Borgne.

New Orleans needed more forts than other cities because of the many waterways -- bayous, bays, lakes, the Mississippi River -- that ran to the city from the Gulf of Mexico.

"The Mississippi River is basically the gateway to the rest of the country. So the river had to be protected," said Joan Exnicios, an archaeologist and historic preservationist with the Army Corps of Engineers in New Orleans. "If you controlled the Mississippi River, you could end up controlling the interior."

So up went Martello Castle and Fort Livingston. Fort Jackson was built on the Mississippi River about 70 miles south of New Orleans, and Fort Pike on the Rigolets to protect the city from an invasion from the north.

Closer to the city, soldiers sweated in the swamps at Fort Macomb, guarding Chef Menteur Pass, yet another way to New Orleans. On Bayou Bienvenue, a battery went up with cannons looking down on the bayou that snakes toward the city from the east.

Several other fortifications -- some built by the French and Spanish in earlier days -- were used and upgraded.

"These forts are in such bad condition," said Raymond Berthelot of the Louisiana Office of State Parks. "The amount of money to stabilize and protect these forts -- we're talking about millions and millions of dollars."

Like the rest of the Louisiana coast, the forts are falling victim to the slow sinking of the Mississippi delta, built up over thousands of years with the accumulation of sediment from the continent's interior.

"Not only are we losing our natural heritage, we are losing our cultural heritage," Berthelot said.

Dennis Eilers, chief landscape architect at the Louisiana Office of State Parks, said his office has talked with Rep. David Vitter (R-La.) and Sen. Mary Landrieu (D-La.) about restoring the coastal forts.

In recent years, limited restoration work was done on Fort Pike -- which is also a state park -- and Fort Livingston. Meanwhile, other forts from the era -- such as Fort Jackson and Fort Macomb -- are not in such bad shape.

About $80,000 in brick restoration went into Fort Pike, and a rock dike was installed in the front of Fort Livingston, which is on Grand Terre Island. The fort has been battered by hurricanes and erosion.

Officials are studying what more can be done at Fort Pike. They estimate that it would cost millions of dollars to restore it.

Plans call for restoring the parapet wall, building the kind of kitchen soldiers would have used back then, installing replica soldiers' quarters, repairing and replacing casements, bringing back the moat and stabilizing the fort.

Stabilizing it will be tricky because the fort was built on a large mat made out of tree trunks -- most likely cypress -- because of subsidence problems even back then.

"From the very outset, we've had problems with flooding and subsidence," Exnicios said.

To justify the renovation costs, officials say, the state could attract military buffs into spending their dollars in the state by highlighting the series of forts.

Eilers said: "The contiguous unit -- that's where the story is."

The interior walls are cracking and crumbling in one of the powder magazines at Fort Pike in Louisiana. Limited repairs have been done.An exterior wall at Fort Pike shows large cracks. State officials say the fort's full restoration would cost millions of dollars.