_Mortar and Cement._--The mortar used by the Byzantine builders was called Keramotos, from the crushed pottery or tiles which was used in its composition. In an article in the _Transactions_ of the Philological Society of Constantinople M. Kouppas[346] enters fully into the methods which have been traditionally followed in cistern building, and describes this mortar as formed of powdered unslaked lime (_asbestos_), crushed pottery, coarse sand, and tow or hair, fully a third being lime, another third the crushed pottery, about a fifth the coarse sand, and the rest or 10 per cent. of hair or tow. These were then mixed together in water. M. Kouppas also describes a hydraulic cement made of “coarse lime (_titanos_) slaked by water into powder, sifted and laid in layers with cotton shreds. This was thoroughly mixed, and then olive oil was poured in, and the whole gradually brought to a homogeneous mass.” Andreossy[347] describes a mixture (called _lukium_) made of a hundred “ocques” of lime, freshly slaked in the form of powder, twenty-five “ocques” of linseed oil of the best quality, and twenty drachms of filaments of cotton. This was reduced to a dough, and then before using fresh oil was added. Strzygowski[348] also speaks of a Turkish cement “of six parts by weight linseed oil, eight parts slaked and powdered lime, and one part of cotton.” He refers to a Roman mixture mentioned by Pliny of “oil and quicklime.” By far the best and earliest account of the methods used for obtaining lime and making cement at Constantinople is contained in Dr. Covel’s MS. in the British Museum (1670-7). The lime was burnt in a pit dug in the ground, the stone, which was hard and black and like “Plymouth stone,” being piled up in and above it like a beehive hut, an opening being contrived in the side for inserting fuel, and a smaller pit dug in the middle for the ashes; it was fired for three days. Then he describes in detail how a cement was made which recalls what the Anonymous says of the joints of the piers at S. Sophia being made of unslaked lime (_asbestos_) and oil: “To make good lukium (a strong cement as I may call it) they take the above said calx or burnt stone and slake it with water, and so soon as it is moulded and turned into a meal (even while it is warm) they work it with linseed oil and cotton till it is well saturated and brought to the consistency of plaster, and make present use of it, for it will not rest in its perfection above one day or two at most, and if they use it immediately after it is tempered it is certainly the best. In the works of their Bagnos so soon as it is laid on [as a plastering, understood here] they let the water come to it, which, by tempering the heat of the lime, hinders it from cracking. Cotton is better to be mixed amongst it than hair, it being more tenacious and apt to incorporate.” He again describes a similar cement (“lukium, an excellent mortar”) used in some waterworks.