Credit: © 2011 GSA

A wealth of tales and historical accounts paints a vivid picture of ancient Greece. The geography revealed by such narratives, however, often bears little resemblance to the Greek isles of today. Sea-level change alone cannot account for the extra islands, suggesting that ancient poets and geographers used a bit of creative licence. But at least in the case of the lost island of Ithaca, the formerly mythological homeland of Odysseus, a closer look suggested similarities between Homer's description of the isle and Paliki peninsula, now part of the island of Kefalonia. A stratigraphic analysis revealed that Kefalonia was once two islands separated by a narrow marine channel. Rockfalls over the intervening years filled the channel and linked the two islands. (Nature Geosci. 2, 455–458; 2009).

Modifications of the landscape by the ancient Greeks themselves turn out to have had similar effects. In the fifth century BC, they built long walls that connected the rocky area of Piraeus to the Greek mainland. Piraeus was formerly an island, but it is unclear whether a connection to the mainland existed before the construction of the walls. Jean-Philippe Goiran of CNRS, France, and colleagues used borehole sediments to reconstruct the joining of the island of Piraeus with mainland Athens (Geology 39, 531–534; 2011).

The sediments reveal a slow and steady progression from isle to mainland. The island stood alone as late as 5,400 years ago. It was still separated from the mainland by a wide lagoon 3,500 years ago, but the shallow basin was periodically filled with sediments from the Cephissus and Korydallos rivers. Sometime before the sixth century BC, the lagoon was replaced by coastal marshes that hosted the walls erected the following century.

Thousands of years later, in the first century AD, the Greek geographer Strabo, who also wrote of the channel separating Paliki from Kefalonia, identified Piraeus as a former island. Whether he knew from Greek oral tradition or just correctly interpreted the relatively flat landscape surrounding the former isle, we will never know. But Strabo accurately captured one era of the rapidly changing landscape of the Greek islands.