floors were usually inhabited by the poor. Till the time of Nero, the streets in Rome were narrow and irregular, and bore traces of the haste and confusion with which the city was built after it had been burnt by the Gauls; but after the great fire in the time of that emperor, by which two-thirds of Rome was burnt to the ground, the city was built with great regularity. The streets were made straight and broad; the height of the houses was restricted, and a certain part of each was required to be built of Gabian or Alban stone, which was proof against fire. The principal parts of a Roman house were the, 1. _Vestibulum_, 2. _Ostium_, 3. _Atrium_ or _Cavum Aedium_, 4. _Alae_, 5. _Tablinum_, 6. _Fauces_, 7. _Peristylium_. The parts of a house which were considered of less importance, and of which the arrangement differed in different houses, were the, 1. _Cubicula_, 2. _Triclinia_, 3. _Oeci_, 4. _Exedrae_, 5. _Pinacotheca_, 6. _Bibliotheca_, 7. _Balineum_, 8. _Culina_, 9. _Coenacula_, 10. _Diaeta_, 11. _Solaria_. We shall speak of each in order.--1. VESTIBULUM did not properly form part of the house, but was a vacant space before the door, forming a court, which was surrounded on three sides by the house, and was open on the fourth to the street.--2. OSTIUM, which is also called _janua_ and _fores_, was the entrance to the house. The street-door admitted into a hall, to which the name of ostium was also given, and in which there was frequently a small room (_cella_) for the porter (_janitor_ or _ostiarius_), and also for a dog, which was usually kept in the hall to guard the house. Another door (_janua interior_) opposite the street-door led into the atrium.--3. ATRIUM or CAVUM AEDIUM, also written _Cavaedium_, are probably only different names of the same room. [Illustration: Atrium of the House of Ceres at Pompeii.]