Biete Mercoreos or Biet Qeddus Mercoreus (House of St. Mercoreos/House of St. Mark) is an Ethiopian Orthodox church located in Lalibela, Amhara, Ethiopia.
It is at the end of the long tunnel which joins the churches of the North-West group to those of the South-East group of which it is a part.
The House of St. Mark (Biete Mercoreos) partly collapsed during an earthquake in the 16th century. A wall was built in the 1980s to close off the remaining part. The church is an underground room with irregular and roughly carved pillars. It measures approximately 25 m considering its extremely irregular shape.
Of older origin than the other churches on the site, the structure could have served primarily for civil or military purposes (or even as a fortified royal residence) and subsequently transformed into a church.
Source: Bete Merqorewos - Wikipédia