Until this week, no one knew about the historical trove waiting inside the former home of a Pennsylvania steel magnate's family.

Except the rats.

Some of the critters had made a nest out of 200-year-old letters and knickknacks in the Coatesville home of the country's first female industrialist, Rebecca Lukens of Lukens Steel Co. fame.

Historians at the National Iron and Steel Heritage Museum in Coatesville on Friday said the letters were among a cache of artifacts, including a mold for making bullets and a buggy whip, found in a wall at Brandywine Mansion.

"It's a time capsule hidden in the walls of the house," said James Ziegler, executive director of the museum. "This will help us to better understand the history of the area and of this plant, and also the economics and industry of that time."

On Tuesday, workers renovating Brandywine Mansion found a stack of at least 10 preserved letters.

During the 1820s and 1830s, when many of the letters were written, Coatesville was a village along the Philadelphia and Lancaster Turnpike, now known as Route 30.

In one letter, a customer ordered an iron plate, with specifications for its dimensions.

Most of the letters found this week are waiting to be opened by experts.

A layer of dust and the dry, dark wall cavity probably preserved many of the missives, said a renovation worker. But some of the letters are too chewed to read.

A small mummified rat was found among the artifacts.

Winterthur Museum near Wilmington will study the relics before the Coatesville museum displays them.