A Byzantine architectural canopy over an altar is called a ciborium.
A ciborium is a freestanding canopy, usually supported by four columns, that marks and visually emphasizes the altar. In Byzantine churches, it could stand beneath or near the sanctuary’s central dome and helped distinguish the most sacred liturgical focus.
The term is sometimes confused with “tabernacle,” which refers to a container for the Eucharist, or with “baldachin,” a broader architectural term for a canopy. Ciboria were used in several Christian architectural traditions, not only Byzantine buildings.
Their form also influenced later church design, including monumental altar canopies in medieval Italy and Renaissance Europe.