SAN ANTONIO (CBSDFW.COM/AP) — An archaeological dig at the Alamo to help preserve the historic Texas mission has unearthed musket balls that experts say could date to the 1800s.

The San Antonio Express-News reports the survey of the mission-era west wall of the Long Barrack is meant to help determine how best to protect the oldest component of the Alamo.

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Crews are digging four pits to help expose the 1700s limestone wall to its foundation in an effort to fight moisture. Archaeologist Kristi Nichols says workers so far have recovered musket balls, a mid-1800s bottle and tin-glazed majolica from the Spanish colonial period.

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The survey began nearly a month ago. Preservation of the Alamo is part of a wider $450 million development plan for the area.