_Hypocausts and Flue Tiles and Wall Linings._—Several examples have been found in London of the Roman system of heating buildings by hypocausts. These were low under-floor spaces a foot or two high connected with an external stoke-hole in one direction and having a flue or flues in the other. When the hypocaust, as was frequently the case, occupied the whole space below a chamber the floor was supported on a large number of roughly-built little piers with a row or two of flat tiles above spanning the intervals, and over them a layer of concrete and a mosaic or other floor. The flues were usually box-tiles, and in the case of the hot chambers of a bath one side of a wall or even more might be lined with them. A hypocaust with its stoke-hole and flue or flues was really a kiln of low power, in which people were warmed on a similar principle to the baking of pottery. The box-tiles were much the shape of a modern brick, and about twice as big; they were hollow and usually had scorings or impressed patterns on the surface to make mortar or plaster adhere (Figs. 6 and 7). Frequently they had a hole or two holes in their narrow sides, so that the mortar might better hold them in place. In the British Museum there is a long and large pipe with ornamental scratchings on the surface which may possibly be a chimney. The system of central heating by the hypocaust seems to have been an admirable contrivance. Lysons illustrated an example at Littlecote where flue tiles ran up in the angles of a room like Tobin tubes, being cased round only by the plaster. The two best known London hypocausts were found in Lower Thames Street and in Bucklersbury. The former extended under the floors of two adjoining apartments. The Bucklersbury example had channels under the floor spreading to several wall flues, each being of two box-tiles placed side by side. (See Price’s account and _V.C.H._) Occasionally flue tiles had two smaller channels; there is a broken example of such a tile in the British Museum. Flue tiles were sometimes of a rounded form ∩, and in this case the wall itself must have served to enclose the flue. In the excavations in Lombard Street in 1785 (_Archæol._ viii.) a brick wall is described which had two flues, one being “semicircular.” A long and well-made ∩-shaped flue in the British Museum, with an impressed lozenge pattern on the surface, is described as a ridge-tile. There is also a fragment of still larger diameter at the Guildhall. Similar flues found at Woodchester were used as horizontal heating channels under the floor.