Corinth was perhaps capital of the Theme of Hellas from the late 7th century and was capital of the Theme of Peloponnese from the early 9th century. Numismatic evidence suggests that the economy of the city began to recover in the 9th century. 
The city of the 11th-12th century differed significantly from late antique Corinth: public buildings (except churches) disappeared, streets became narrow, and the old Roman marketplace was covered by small shops. Shops also moved to colonnades along the major streets, and tombs slowly began to encroach upon the ancient civic center. From the 9th century onward the settlement abandoned the ancient city plan, as shops, workshops, gardens, churches, and monasteries jostled one another without any apparent order. Workshops for the production of ceramics (with remains of kilns) and glass, as well as smithies, have been excavated. Narrative sources emphasize the existence of a flourishing silk industry in the 12th century. The city continued to function as an important harbor. 
In 1147 Roger II of Sicily attacked Corinth: the inhabitants fled to Acrocorinth, which fell as a result of the incompetence of the commander Nikephoros Chalouphes. Roger carried off both Corinthian notables and artisans (particularly the city's famed silk weavers) as well as considerable wealth, including an icon of St. Theodore. The city apparently did not fully recover from the sack of the Normans. Leo Sgouros took Corinth in 1202. In 1205 the Crusaders, nominally under the authority of Boniface of Montferrat, began a siege of Acrocorinth, defended by Sgouros. The attackers built a castle at Penteskouphi, but the siege dragged on until around 1210 when Theodore Komnenos Doukas, brother of despot Michael I of Epirus, gained control of Acrocorinth, presumably by treaty.
The city became part of the Principality of Achaia. Little is known of Corinth under Frankish rule, as it was not one of the great baronies; the mint was, however, located at Corinth until it was moved to Clarence (Clarenza). The city and castle were formally surrendered to the Byzantine in 1262 by William II Villehardouin, but the local commander refused to relinquish control. Corinth was ceded to Philip I of Taranto around 1300 and in 1305 a great tournament was held at the Isthmus. In 1358 the city was given to Niccolò Acciajuoli, who strengthened the defenses. In 1395 Theodore I Palaiologos, despot of the Morea, gained control of Corinth for the Byzantines. In 1397 he surrendered the city to the Hospitallers, who held it until 1404, when they returned Corinth to Byzantine control. Around 1443 the future emperor Constantine XI appointed a certain John Kantakouzenos as governor in Corinth. The territory was ravaged by the Ottomansin 1446. Mehmed II attacked the city in 1458, and in August the residents surrendered Acrocorinth to him. 
The bishop of Corinth was metropolitan of the Peloponnese and of the Province of Achaia. He was present at most of the early councils. In 431 he was the only bishop from the Peloponnese and in 680 the only representative from Greece. In the crisis after the Slavic invasions the bishop of Patras contested control over the Peloponnese with Corinth, and in the 10th century the suffragans of Corinth were restricted to the eastern Peloponnese and the Ionian Islands. There was a sizable monastery of St. John in the area of the ancient center, and literary sources and seals refer to an important Church of St. Theodore whose site has not been identified. None of the Byzantine churches of Corinth has survived intact. The fortifications of Acrocorinth rest largely on ancient foundations, but many sections of Byzantine masonry, probably of the 6th-7th centuries, can be seen, especially along the inner western wall.