A belt course, also called a string course or sill course, is a continuous row or layer of stones or brick set in a wall. Set in line with window sills, it helps to make the horizontal line of the sills visually more prominent. Set between the floors of a house, it helps to make the separate floors distinguishable from the exterior of the building.
Although the belt course has its origins as a structural component of a building, by the 18th century it was almost purely a decorative element and had no functional purpose. In brick or stone buildings taller than three stories, however, a shelf angle is usually used to transfer the load of the wall to a hidden, interior steel wall. Flashing is used to cover the space exposed by the shelf angle to help limit the intrusion of water. Where flashing is considered aesthetically unpleasing, a belt course is often used.