Story highlights The time capsule was buried deep in a Confederate monument in St. Louis

The capsule dates to 1914, and many of its contents remain a mystery

(CNN) Workers taking down a controversial Confederate monument in St. Louis have discovered a 102-year-old time capsule buried in its base.

Removal of the Confederate Memorial in Forest Park began Monday as part of an agreement between St. Louis and the Missouri Civil War Museum.

The copper time capsule was sealed in the center of the very bottom of the monument about a month before it was completed, said Mark Trout, executive director of the Missouri Civil War Museum, who knew about the capsule's existence from historical documents.

"We knew it was in there somewhere, so we were careful as we chipped away at something like 40 tons of concrete until we got to the very bottom," Trout said.

There, workers found a stone tablet that read, "On this spot, a monument will be erected in memory of the soldiers and sailors of the Confederacy." The monument was dedicated in 1914.

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