have been made of wrought iron. But
perhaps they more than compensated for these evil contrivances by the
introduction of the mariner's compass.

[Sidenote: Their commerce.] The mention of the mariner's compass might
lead us correctly to infer that the Spanish Arabs were interested in
commercial pursuits, a conclusion to which we should also come when we
consider the revenues of some of their khalifs. That of Abderrahman III.
is stated at five and a half million sterling--a vast sum if considered
by its modern equivalent, and far more than could possibly be raised by
taxes on the produce of the soil. It probably exceeded the entire
revenue of all the sovereigns of Christendom taken together. From
Barcelona and other ports an immense trade with the Levant was
maintained, but it was mainly in the hands of the Jews, who, from the
first invasion of Spain by Musa, had ever been the firm allies and
collaborators of the Arabs. Together they had participated in the
dangers of the invasion; together they had shared its boundless success;
together they had held in irreverent derision, nay, even in contempt,
the woman-worshippers and polytheistic savages beyond the Pyrenees--as
they mirthfully called those whose long-delayed vengeance they were in
the end to feel; together they were expelled. Against such Jews as
lingered behind the hideous persecutions of the Inquisition were
directed. But in the days of their prosperity they maintained a merchant
marine of more than a thousand ships. They had factories and consuls on
the Tanais. With Constantinople alone they maintained a great trade; it
ramified from the Black Sea and East Mediterranean into the interior of
Asia; it reached the ports of India and China, and extended along the
African coast as far as Madagascar. Even in these commercial affairs the
singular genius of the Jew and Arabs shines forth. In the midst of the
tenth century, when Europe was about in the same condition that
Caffraria is now, enlightened Moors, like Abul Cassem, were writing
treatises on the principles of trade and commerce. As on so many other
occasions, on these affairs they have left their traces. The smallest
weight they used in trade was the grain of barley, four of which were
equal to one sweet pea, called in Arabic carat. We still use the grain
as our unit of weight, and still speak of gold as being so many carats
fine.

[Sidenote: Obligations to the Khalifs of the West.] Such were the
Khalifs of