Known. Carbon in the mortar dates this fort to the Teutonic Knights.
The fort is Feldioara, also called Marienburg, in Brasov County, Transylvania, Romania. The knights were there from 1211 to 1225, in the 13th century. A Hungarian king, Andrew II, invited them. They built earth walls, a wooden fort, and a stone base. Tests on thirteen mortar samples were set against those years.
One sample from under the church may be from building work before the knights arrived.