Corfu is a Greek island in the Ionian Sea. It is the second largest of the Ionian Islands, and, including its small satellite islands, forms the edge of the northwestern frontier of Greece. The island is part of the Corfu regional unit, and is administered as a single municipality. The municipality includes the island Corfu and the smaller islands Ereikoussa, Mathraki and Othonoi. The principal city of the island and seat of the municipality (pop. 33,886) is also named Corfu. Corfu is home to the Ionian University. The island is connected to the history of Greece from the beginning of Greek mythology. Its Greek name, Kerkyra or Korkyra, is related to two powerful water symbols: Poseidon, god of the sea, and Asopos, an important Greek mainland river. According to myth, Poseidon fell in love with the beautiful nymph Korkyra, daughter of Asopus and river nymph Metope, and abducted her. Poseidon brought Korkyra to the hitherto unnamed island and, in marital bliss, offered her name to the place: Korkyra, which gradually evolved to Kerkyra. Together, they had a child they called Phaiax, after whom the inhabitants of the island were named: Phaiakes. This term was transliterated via Latin to Phaeacians. The island's history is laden with battles and conquests. The legacy of these struggles is visible in the form of castles punctuating strategic locations across the island. Two of these castles enclose its capital, which is the only city in Greece to be surrounded in such a way. As a result, Corfu's capital has been officially declared a Kastropolis ("castle city") by the Greek government. Corfu was long controlled by Venice, which repulsed several Turkish sieges, before falling under British rule following the Napoleonic Wars. Corfu was eventually ceded by the British Empire along with the remaining islands of the United States of the Ionian Islands, and unification with modern Greece was concluded in 1864 under the Treaty of London. In 2007, the city's old city was designated for the UNESCO World Heritage List, following a recommendation by ICOMOS. Corfu is a very popular tourist destination. Up until the early 20th century, it was mainly visited by the European royals and elites, including Emperor Wilhelm II of Germany and Empress Elisabeth of Austria; today it is also widely visited by middle class families, leading to mass tourism. It is still popular with the global elite however, and in the island's northeast the homeowners include members of the Rothschild family and Russian oligarchs.