BOOK VII	165
	side. Later, when they finally dry the inside shrinks and breaks the dry outer crust producing numerous cracks and weakening the brick. There are four varieties of bricks, first, those used in walls, second, those used for battlements on the top of walls, third, those spread on the ground, and fourth, those used for roofs. There are three types of bricks used in Avails, following the usage of the Greeks who have given names to them. One is called δίδωρον, being two palms (about six inches) wide, whence the name, and twelve inches long. The Greeks call a palm length δώρον. The second type, twelve inches long and twelve inches wide is called πτράδωρον. The third, fifteen inches in each direction is called πντάδωρον. The ancient peoples used unbaked bricks but let them stand two years before they were used. According to Vitruvius the people of Utica let their bricks stand for five years so that they would become thoroughly dry. This type can be seen today in certain villages of Bohemia. The Germans use burnt bricks. Care must be taken when burning them. If they are burnt too much they have a glassy appearance and will not take mortar while if they are under-burnt they are fragile and the lime in the mortar will fracture them. Neither is suited for building. The bricks used for battlements are made in a variety of forms. They may have projections added to them after they are made and they may be shaped into semicircles. The exposed portion of the brick may be given various colors or smeared with litharge to give it a glassy appear­ance. The bricks used for paving are usually square and three to nine inches on the side although the thick bricks are usually only three inches. The bricks we see paving the roads of the Venetians are thicker and closely fitted in order to reduce the wear by pedestrians. The exposed side of the brick may be colored in order to give a more pleasing appearance. The bricks used to cover the roofs of houses are either tabular like the tongue or concave like a pipe. The younger writers call the former lingua, the latter prisons imbrex17 because the rain runs off along these just as along a canal. At one time they made half-bricks for use in Avails and today half-bricks of the lingua type are made and used for roofing houses. Many fa­mous buildings in Germany, especially in Saxony and Misena, are built of brick. The Avail betAveen the city of Leipzig and the monastery of St. Paul is Avell known. The toAArn of Urbino, Picenum, has a famous brick fortress. This Avas built by the very renoAvned and brave Prince Fredrick Maria. Brick walls, as Pliny AATites, will last forever if built vertical. Ac­tually they last so well they are used in public buildings and royal homes. The Avail of Athens facing Mt. Hymettus was built of brick as well as the temples of Jove and Hercules at Patras although these are surrounded by stone columns and architraves. Other famous buildings are the royal home of Attalus at Tralles, the royal home of Croesus at Sardes which
	17 Ancient hollow tile.