Southernmost peninsula of Greece, also known from the Frankish period as the Morea.
In late antiquity part of the province of Achaia, the Peloponnesos retained its urban character: Hierokles counted 26 cities in the Peloponnesos.
From the late 6th century, however, building activity in the peninsula practically stopped: it is still unclear whether this economic decline resulted from hostile invasions, primarily Slavic, or "was also caused by a more general phenomenon of decline" (Lemerle).
The question of the Slavic invasion has been hotly discussed. Slavic penetration in the Peloponnesos is indicated by the evidence of toponyms -M.Vsmer (Slaven) counted 429 place names of Slavic origin in the Peloponnesos, although some dozens could be disputed. TheSlavs seem not to have occupied the eastern cities, however, and they underwent rapid hellenization, even though in the 14th century there were independent Slavic communities in the peninsula.
From the late 7th century the Peloponnesos was part of the theme of Hellas, and from the early 9th century it was a theme in it own right, with its capital at Corinth: Leo Skleros may have been the first 'strategos'.
The coasts of the Peloponnesos were ravaged by Arab pirates in the 9th and 10th centuries until theByzantine reconquest of Crete in 961.
After that the peninsula prospered , with plentiful evidence of rich agricultural production, commerce, and industry in cities such as Corinth and Patras.
Beginning in 1205 the leaders of the Fourth Crusade, notably William I of Champlitte and Geoffrey I Villehardouin captured most of the Peloponnesos without serious struggle, and the land was divided into baronies, loosely under the authority of the principality of Achaia. The conquest was completed by 1248, but the Frankish defeat at the battle of Pelagonia in 1959 and the surrender of Mistra and other territories with the Treaty of Constantinople in 1262 initiated the revival of Byzantine power in the Peloponnesos -henceforth divided between the despotate of the Morea and the various Frankish states.
The Turks entered the peninsula in 1446 and, except for Venetian strongholds such as Nauplia and Methone, conquered the entire Peloponnesos by 1460.
The bishop of Corinth, originally metropolitan of Hellas and of the Peloponnesos, was challenged, especially by the metropolitan of Patras. Overtime the bishops of Lakedaimon, Argos, and Christianoupolis also gained metropolitan status.
Oxford Dictionary of Byzantium (1991), vol.3, p.1620