Crassus (2.5-2.6)

But though he owned so many artisans, he built no house for himself other than the one in which he lived; indeed, he used to say that men who were fond of building were their own undoers, and needed no other foes. And though he owned numberless silver mines, and highly valuable tracts of land with the labourers upon them, nevertheless one night regard all this as nothing compared with the value of his slaves;

so many and so capable were the slaves he possessed,—readers, amanuenses, silver- smiths, stewards, table-servants; and he himself directed their education, and took part in it himself as a teacher, and, in a word, he thought that the chief duty of the master was to care for his slaves as the living implements of household management.