It is true that a considerable number of persons, absolutely speaking, have amassed great wealth out of land. It is a well known fact that land was the principal source of the great mediæval and post-mediæval fortunes, down to the end of the eighteenth century. "The historical foundation of capitalism is rent."[73] Capitalism had its beginning in the revenue from agricultural lands, city sites, and mines. A conspicuous example is that of the great Fugger family of the sixteenth century, whose wealth was mostly derived from the ownership and exploitation of rich mineral lands.[74] In the United States very few large fortunes have been obtained from agricultural land, but the same is not true of mineral lands, timber lands, or urban sites. "The growth of cities has, through real estate speculation and incremental income, made many of our millionaires."[75] "As with the unearned income of city land, our mineral resources have been conspicuously prolific producers of millionaires."[76] The most striking instance of great wealth derived from urban land is the fortune of the Astor family. While gains from trading ventures formed the beginning of the riches of the original Astor, John Jacob, these were "a comparatively insignificant portion of the great fortune which he transmitted to his descendants."[77] At his death, in 1848, John Jacob Astor's real estate holdings in New York City were valued at eighteen or twenty million dollars. To-day the Astor estate in that city is estimated at between 450 and 500 millions, and within a quarter of a century will not improbably be worth one billion dollars.[78] According to an investigation made in 1892 by the _New York Tribune_, 26.4 per cent. of the millionaire fortunes of the United States at that time were traceable to landownership, while 41.5 per cent. were derived from competitive industries which were largely assisted by land possessions.[79] The proportion of such fortunes that is due, directly or indirectly, in whole or in part, to landownership has undoubtedly increased considerably since 1892.