According to the Bradt Guide Ethiopia by Phillip Briggs (4th ed., November 2005),
"Bet Mercurios is a cave church.  It was orginally used for secular purposes, and may well be around 1,400 years old.
A fifteenth-century wall frieze inside Bet Mercurios, one of the oldest chambers in the Lalibela complex. Originally a cave used for secular purposes, the space was later consecrated as a church and decorated with painted panels depicting saints and biblical scenes. © A. Davey from Where I Live Now: Pacific Northwest, CC BY 2.0, via Wikimedia Commons

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