66 PIAST
between Poland and the west. Best known of them, however, was Witello or
Vitellon (1230-80), a Silesian philosopher active in the second half of the thir-
teenth century, who was an associate both of William of Moerbecke and of
Thomas Aquinas. The son of a German colonist from Thuringia and of a Polish
mother, he spent the first part of his career in a Polish monastery before depart-
ing for Italy. His fundamental treatise on the science of optics, the Perspectiva,
was inspired by the belief that an enquiry into the physical properties of light
would solve the metaphysical problem of the nature of existence. His study of
human sight led him to the distinction between the mechanical operations of the
eye and the co-ordinative subconscious functions of the mind. In this way, he is
sometimes seen as one of the precursors of modern psychology.^4
The incorporation of the cities probably provided the immediate cause for
the granting in 1264 of a General Charter of Jewish liberties by Boleslaus the
Modest, Prince of Cracow. There is little reason to doubt that Jews had lived in
Poland from the earliest times, and that Judaism, as preserved by the descen-
dants of the ancient Chazar kingdom in the south-east, had actually antedated
Christianity. But no separate legal provisions were necessary until the mid-
thirteenth century when the new powers of city corporations might have been
used to harass the Jews or to exclude them altogether. As a result, the General
Charter specifically listed the right of the Jews to travel round the country with-
out molestation; to engage in trade; to pursue their own religious practices,
including worship in their synagogues, Jewish burial, and ritual slaughter; and
to be exempted from slavery or serfdom. It could not insist, of course, that the
Jews be allowed to reside within the bounds of the city, or that they should
enjoy the same rights as those of the autonomous Christian burghers. But it pro-
vided the basis of later Jewish prosperity in Poland, and served as the model for
all subsequent re-confirmations of Jewish liberties by Polish rulers until the end
of the eighteenth century.^5
In this same era, economic life made rapid advances. The revolution in farm-
management, first demonstrated by the Cistercians spread quickly into the sec-
ular estates and encouraged the concentration of land holdings in compact
units. Bishops, barons, and royal bailiffs, all competed to maximize the output
of their lands. All raised their demands on the peasantry. The incorporation of
cities in the thirteenth century, was encouraged by the previous functioning of
some three hundred chartered markets and by a growing network of roads,
horse transport, and storage depots. At the same time, the progress of coloniza-
tion assisted the growth of a cash economy. Internal trade increased. Mining
under royal auspices at Wieliczka for salt, at Olkusz for lead and tin, and at
Kielce for iron, was expanded. The ancient system of coinage was reformed.
The first Polish denarii (silver pennies) had been struck in the 980s by Mieszko
I. Survivals from the reign of Boleslaw Chrobry with inscriptions such as
'PRINCES POLONIE' or 'GNEZDUN CIVITAS' are well known. But the
'thick pennies' of the early Piasts had been repeatedly used to remit more and
more 'thin pennies' of the later principalities. In 1337-47, the new coinage was