ST. LOUIS COUNTY • Police are looking for the thief or thieves who took six rare Civil War-era gold and silver U.S. coins from the Museum of Transportation over the weekend.

Museum staff and police believe a silver dollar and five gold coins dating back between the 1840s through the 1860s were stolen Saturday or Sunday from glass display cases in a traveling exhibit, "Money of the U.S. Civil War," commemorating the 150th anniversary of the Civil War.

"They're irreplaceable," said Kristen Valenti, special projects coordinator for the museum at 3015 Barrett Station Road. "We're just concerned with getting the artifacts back."

Workers discovered the coins missing shortly before the museum opened at 11 a.m. Sunday. Valenti said employees believe the coins were last seen in four display cases late Saturday afternoon before the museum's 5 p.m. closing time.

Police said there was no evidence of a break-in at the museum.

Workers set up the exhibit Friday morning on a second-floor mezzanine in the museum's Earl C. Lindburg Automobile Center. The exhibit, on loan from the American Numismatic Association Money Museum in Colorado Springs, Colo., was set to open Monday and run through June 30.

Museum president David Ahner said the coins' historical value ranged between $1 and $20 each. But today, he said "these are priceless."

Ahner said it appears the key locks on the display cases were picked.

During business hours, security guards patrol the museum but are not stationed directly by the coin display, Valenti said. The museum is locked and protected by an alarm system when closed.

Valenti said the six stolen coins were the most valuable part of the exhibit, which included other Civil War-era coins, paper currency used by the Confederates and other artifacts.

The theft of the coins "robs a piece of American history and the nation," Valenti said.

The exhibit is still open to the public but the museum, for security reasons, has substituted the remaining 21 coins with pictures and poster boards describing the items in the collection, Valenti said. Meanwhile, the exhibit will be moved to a more secure area that will be monitored by staff during business hours.

"These coins are an important piece of our collective history," Ahner said. "They must be returned so future generations can appreciate our nation's past."

Ahner said the museum is offering a $1,000 reward through Crimestoppers for information that helps return the coins. He said the museum would not ask for criminal charges if the thief or thieves simply returned them.

"I just want the coins back," he said.

Anyone with information about the theft is asked to call St. Louis County Police at 314-889-2341 or CrimeStoppers at 1-866-371-8477. For more information about the museum, visit its website here.