The rest of Crassus's wealth was acquired more conventionally, through traffic in slaves, the working of silver mines, and judicious purchases of land and houses, especially those of proscribed citizens. Most notorious was his acquisition of burning houses: when Crassus received word that a house was on fire, he would arrive and purchase the doomed property along with surrounding buildings for a modest sum, and then employ his army of 500 clients to put the fire out before much damage had been done. Crassus's clients employed the Roman method of firefighting—destroying the burning building to curtail the spread of the flames.[7]