The earliest history of Corfu relates back to the Phaeacians, where the island is believed to be the location of Sceria where Odysseus encountered the young girls including Athena dressed up as one of the girls.
For linkages between The Odyssey and Corfu go to: https://en.wikipedia.org/wiki/Scheria
For more details about Corfu, go to: https://en.wikipedia.org/wiki/Corfu
From medieval times and into the 17th century, the island was recognized as a bulwark of the European States against the Ottoman Empire and became one of the most fortified places in Europe. The fortifications of the island were used by the Venetians to defend against Ottoman intrusion into the Adriatic. Corfu repulsed several Ottoman sieges, before passing under British rule following the Napoleonic Wars.
Kerkyra, the "Door of Venice" during the centuries when the whole Adriatic was the Gulf of Venice, remained in Venetian hands from 1401 until 1797, though several times assailed by Ottoman naval and land forces and subjected to four notable sieges in 1537, 1571, 1573 and 1716, in which the strength of the city defences asserted itself time after time.