Excavations at the medieval fortress of Rusokastro in southeastern Bulgaria uncovered a monumental stone building with walls coated in waterproof pink mortar, a rare detail that draws attention from anyone who works with historic masonry.
The Regional Historical Museum of Burgas reported that the structure sits near the inner southern defensive wall, in an area researchers describe as the central district of the medieval city. The building measures 7.60 meters (25 feet) across, with its full length still under investigation. Its stone walls are about 1.10 meters (3.6 feet) thick, with heavy mortar joints binding the masonry.
The standout feature is a thick layer of pink, hydrophobic mortar on the interior faces of the walls. Researchers link that water-resistant coating to a ground floor designed for utility, not just living space. Their working interpretations focus on storage, either as a reservoir or a space for holding food supplies. Investigators also believe the surviving remains represent the ground floor of a larger building, with a residential level once above it.
Archaeologists also recovered portable finds, including silver coins issued under Tsar Ivan Alexander, Venetian silver grossi known as matapans, and copper coins. Ivan Alexander ruled from 1331 to 1371, and he is tied to a defining moment at Rusokastro, the July 18, 1332, victory over the Byzantine army led by Emperor Andronikos III Palaiologos. Museum staff noted that the coins’ exact contexts remain separate from the battle narrative while conservation specialists clean and examine them.
For mason contractors and restoration teams, the takeaway is straightforward: historic builders treated mortar and interior coatings as performance materials, especially inside fortified infrastructure.
Document mortar color, texture, and thickness during investigations.
Track how wall coatings relate to drainage, storage, and long-term moisture exposure.
Read the full, original article from Arkeonews here.