File:Roman tile, Box flue tile (FindID 877605).jpg

A fragment of a Roman ceramic relief-patterned box flue tile dating from AD 50-400. The front is decorated with a relief-patterned rolled design in the chevron style. Betts writes that flue tilese were "keyed with wooden rollers [...] when the clay was still damp, before they were put into the kiln to fire. This was added so the tiles could be more firmly mortared into place." The fabric is fully oxidised throughout and has infrequent inclusions of iron and rare small grit / stone.

McComish (2015:12) writes "Box flues (tubuli) are hollow rectangular or square cross-sectioned tiles, with sanded interior surfaces, and they have vents in two opposing sides, while the other two sides are usually keyed. The keying can be incised, finger drawn, combed, or relief-patterned. There is no standard size for box flue tiles nationally (ibid., 74). Box flues were made by wrapping a slab of clay around a sanded former then joining the edges of the clay together with a single seam, and the vents were cut out after the tile was removed from the former (Rudling et al. 1986, 204)."