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 44 A HISTORY OF THE CRUSADES 
 That all-important city the Arabs besieged by land and sea for over a year;
not until famine and pestilence had decimated some of their forces, and a
Byzantine-Venetian fleet threatened the rest, did they raise the siege. They
burned their own ships and fled into the interior; driven from Mineo and
Enna and abandoning Agrigento, they returned to Mazara, their starting point
two years before. Spanish Arabs, who unexpectedly appeared for purposes of
plunder, supported the retreating Aghlabids, renewed the attack, and plundered
as far as Mineo, but then retreated to Mazara, whence they sailed to Spain.
At the same time, in 828, a Frankish fleet under count Boniface of Tuscany
cleared the waters around Corsica and Sardinia and successfully plundered
the African coast between Utica and Carthage. Byzantine land and sea forces,
aided by the Venetians, had frustrated for the moment the Arab conquest of
the island. 
 The second effort at conquest, however, succeeded and eventually led to
the occupation of the entire island. In 830 an African fleet of three hundred
ships and some Spanish squadrons attacked and besieged Palermo, the second
city on the island. After a year the strategic port fell to the besiegers,
for whom it became the base of operations against the rest of the island
and, more significantly, against the mainland. In spite of active Byzantine
resistance and occasional successes the Arabs consolidated and increased
their holdings. They took a decade to drive out stubborn garrisons and to
capture strongholds; by 840 they controlled western Sicily and could turn
to other parts of the island. In 843 they captured Messina after a long siege
and a surprise land attack; with its capture they controlled the Strait of
Messina and so could prevent the entrance of Byzantine naval forces jnto
western waters. Actually, they were assisted by the Neapolitans, on whose
behalf they had intervened against duke Sikard of Benevento, when the latter
had laid siege to their city in 837. Not only political, but economic considerations,
too, prompted the Christians of Naples to aid the enemy, for only in friendly
alliance with the Arabs were they able to carry on their commerce since the
eastern Mediterranean was already closed to them, by other Arabs and by the
Venetians.2 
 With Palermo and Messina in hand, the Arabs turned to the southeastern part
of the island, especially toward Syracuse. They 
 2 Both Pirenne and Gay emphasize the commercial reasons for these alliances
with the Arabs. Henri Pirenne, Mohammed and Charlemagne (New York, 1939),
pp. i8zf. Pirenne 
quotes J. Gay, L'Italie méridionale et l'empire byzantin (Paris, 1904),
p. 529. A very recent and concise review of Moslem trade has been made by
Robert S. Lopez in Cambridge Economic History, II (Cambridge, 5952), z8 5—289.