The houses in which the ordinary Roman lived were chiefly built of wood: only very rich men had stone or marble houses at this time. The streets were extremely narrow, and many of them very steep and crooked, and the dwellings, whether single houses or great tenements, were crowded closely together. As the buildings grew old they were apt to fall down, especially the high flats, which became top-heavy. Serious fires were also very common. Crassus observed this. He therefore collected a great body of slaves, skilled as carpenters and masons. He also equipped others as a fire brigade. When a fire broke out anywhere he would make an offer to the owner to buy the house very cheaply. Were his offer accepted he would put out the conflagration and rebuild. Were it refused he would let it burn. At the same time he bought up at cheap rates houses in bad repair and likely to collapse, which he therefore got at low prices. In this way he became owner of a great part of Rome, and, as more and more people were constantly crowding into the city to live, and the supply of houses was less than the demand for them, he could and did charge high rents. People who refused to live in his houses could find nowhere else to go. This was one of the means by which Crassus acquired his riches. But he was incessantly alert and active to spy out opportunities in this direction or in that for making money. His energy never relaxed: he was always busy. He never fell into idle ways or the kind of stupid amusement in which so many Romans, young and old, frittered away most of their time. At a time when he owned half the houses in Rome, and so many members of the Senate were in debt to him that they dared not vote against his wishes, he built for himself only one house, and that of moderate size. He enjoyed money-making as men enjoy any pursuit of which they are master. After a time, however, he grew so rich that a new ambition seized him. He began to thirst after direct political power--not merely the indirect power which his money gave him. Crassus was no fool. In financial affairs of all kinds he had courage, resource, ingenuity, determination, and persistence, with that touch of imagination which belongs to any kind of genius. It was not only by accident that everything he touched turned to gold. But his imagination was of a narrowly limited kind. He understood all the lower motives that move men but none of the higher ones, for he understood only what he found within himself, and within himself there was no room for the power of any kind of idea.