The river mouth has progressively moved east. About 12,000 years ago it used to enter the sea five kilometres further west, where Grado stands today, and where there are still some barely discernible reliefs of fluvial deposits, inland at San Marco and Belvedere, and in the lagoon in the form of the islets of Gorgo and Lovo. In Roman times, it flowed close to the Karst into Lacus Timavi. In the Middle Ages, the Natisone joined the Isonzo and together flowed into the sea east of Grado. The maps of the sixteenth century show the Isonzo flowing in what is today the Isonzato, which then moved east into the current Sdobba course, within the bed of a river resulting from springs. During a flood in 1490, the Isola Morosini was formed between the Isonzato and Sdobba,. In maps of 1740, a watercourse resulting from springs is shown east of Sdobba, called “Correntia” but in 1895, this vanished when the Isonzo broke into the bed and took it over. This became the main branch of the river mouth, which was later called Quarantia. Between the Sdobba and Quarantia, the Cona island was formed. In 1934, the Quarantia was closed with an embankment to prevent silting of the bay of Panzano, and bringing the river mouth back to the Sdobba bed.