Through the Đerdap Strait, the Pannonian Sea was connected to another sea located in Wallachian-Pontic Basin. During its largest geographical extent, the Pannonian Sea reached the south of modern Serbia: a gulf of the Pannonian Sea located in modern Morava river valley stretched to modern Grdelica Gulch and Vranje Depression and was connected to the Aegean Sea through the modern Preševo Valley.
The Pannonian Sea existed for about 9 million years. Its last remains disappered in the middle of Pleistocene Epoch, about 600,000 years ago. The water of the Pannonian Sea actually ruptured its way through the modern Đerdap Gorge on the Danube river and flowed through the gorge leaving behind a large plain known as the Pannonian Plain. The remnants of the former islands of the Pannonian Sea are modern Pannonian Island Mountains (Fruška Gora and Vršac Mountains).