Michael Nixon and Richard Lang looked out the second-story window of the Hilton Pittsburgh hotel yesterday and scowled as if they were watching the Indians descend on Fort Pitt in 1763.

A contractor this week began filling in the fort's Music Bastion wall and old moat, part of what state officials call a $35 million improvement project to Point State Park. Critics, including Mr. Nixon and Mr. Lang, have other terms for it.

"They're converting a memorial park to a carnival use, which is inappropriate," said Mr. Nixon, who described himself as a national historic preservation lawyer and consultant.

Burying the wall and moat, across from the Hilton, will create a larger lawn space for community events. The project also will involve new walkways, lighting and signs and wireless Internet access, said Christina Novak, spokeswoman for the state Department of Conservation and Natural Resources.

Ms. Novak said the wall and trench will be filled in a way that preserves the site in case somebody, sometime, wants to excavate it again. The Pennsylvania Historical and Museum Commission supports the project, she said, and the Riverlife Task Force and Allegheny Conference on Community Development had planning input.

Supporters see the park project as a way to burnish the city's showpiece. But Mr. Nixon and Mr. Lang, who was the Carnegie Museum's crew chief on the Music Bastion excavation in the 1960s, complained that an archaeological treasure is giving way to corn-dog stands.

Mr. Nixon said the fort, which survived the siege during the French and Indian War, was the largest British stronghold in North America and an early site of germ warfare. The British commander reportedly gave two smallpox-exposed blankets to the Indians.

While they would prefer the wall remain uncovered, Mr. Nixon and Mr. Lang also are dissatisfied with safeguards the state agencies have planned to protect it below ground.

Initial plans called for fill -- a mix of concrete, asphalt and soil from other areas of the park -- to be placed atop a "thick, felt-like" protective blanket in the trench and along the wall. Officials of DCNR and the museum commission last week met in Harrisburg to discuss the work and yesterday announced additional safeguards -- a foot-thick mixture of sand and gravel and a second layer of fabric to give the wall more padding.

Because burial of an archaeological site is unusual, Mr. Nixon said, the agencies should have developed a more careful plan and exposed it to a professional-review process.

Mr. Nixon said he feared the wall would be damaged by vibrations from heavy equipment used to break concrete and asphalt into fill. He said the textile should be bright orange, instead of black or gray, to better separate the fill from Mr. Lang's excavation.

He and Mr. Lang also have contended that a better-quality fill, not debris from the park renovation, should be placed in the trench. Mr. Nixon said the museum commission has violated its public trust by endorsing the project.

But commission spokeswoman Jane Crawford said state agencies are committed to the wall's preservation. Last week's meeting and the new safeguards, she said, are evidence of that.

A second phase of the project, to include better river access and improvements to the park fountain, has not been scheduled. The first phase, including burial of the wall and moat, is to be completed by the end of 2007.