03/11/2026
20,000 years ago, Naxos, Paros, Mykonos, Tinos, Andros and Ios were not separate islands. They were one.
During the last Ice Age, so much of Earth's water was locked up in ice sheets that sea level in the Aegean was about 120 metres (390 ft) lower than today. The shallow seafloor between these Greek islands dried out and joined them into a single big island. Scientists call it the "Mega-Cyclades palaeo-island".
Which islands joined is measured on the seafloor data used for this map: 26 of today's islands (each bigger than 1 km²) merge into one island of about 6,900 km², almost four times their land area today. A 2017 study that modelled local sea levels across the Aegean (Simaiakis et al.) goes further: it counts more than 55 of today's islands inside the old island and finds it shrank from about 10,750 km² to 3,250 km², a loss of 75%.
Not every island joined. On this map, Santorini, Milos, Sifnos and Serifos sit across deeper water (170 m or more) and stay separate. Santorini is drawn with its present-day shape; as a volcano, its outline has changed since.
The old island had its own wildlife. Fossils on Naxos belong to a dwarf elephant only about a tenth the size of its mainland ancestor, probably from the late part of the Ice Age.
Then the ice melted and the sea rose, cutting the big island into the archipelago we know today. The 2017 study finds the biggest and fastest changes across the Aegean islands came between about 16,000 and 8,000 years ago.
The dashed line on the left map is today's coastline. Everything between it and the Ice Age sea is now under water.
Note: the left map floods today's seafloor to 120 m below present sea level, so the old coastline is approximate. It doesn't account for sediment laid down or land movement since then, and the Aegean is tectonically active. On both maps the sea is shaded by depth. Areas and island counts on the map are measured from the map data.
📍 Cyclades, Aegean Sea, Greece
🛰️ Contains modified Copernicus Sentinel data (August-September 2026). Seafloor: EMODnet Bathymetry.
Facts: Simaiakis et al. 2017, Palaeogeography, Palaeoclimatology, Palaeoecology (doi 10.1016/j.palaeo.2017.02.002); Kapsimalis et al. 2009, Zeitschrift für Geomorphologie; van der Geer et al. 2014, Palaeogeography, Palaeoclimatology, Palaeoecology (Naxos dwarf elephant); Wikipedia (Dwarf elephant).