Waves

Wind stress, the drag or tangential force exerted on the earth's surface by adjacent layers of moving air, is the principal engine of oceanic wave formation (Morton 2001: 30—37). These waves travel in the direction of the wind, gaining height and strength so long as the wind continues in the same direction and the waves do not encounter topographic obstructions. Once the wind stops or changes direction, the wave continues some distance under its own momentum, sometimes causing the clashing of waves moving in different directions. The gales, squalls, and other stormy weather typical of the Aegean can produce rough seas with high waves and swells. Because of the irregular pattern of wind flows and gusts, waves in the open Aegean tend to be choppy, short-frequency waves that would have been dangerous for the small craft of the Bronze Age (Broodbank 2000: 101). The concentration of stormy weather and rough seas in winter explains the general avoidance in antiquity of open-sea sailing in the Aegean from October to March. Once waves approach coastal areas, they are affected by several factors that determine their contact with the coast and the effects they might visit upon watercraft and coastal settlements. Among these factors are the form and magnitude of the wave, measured by wave height and wavelength; wind speed and direction; the angle of contact with the coastline; and surface and subsurface topography along the coast. The configuration of the coastline, including its shape and the extent and form of any submarine coastal shelf, may serve to magnify or minimize the force of waves breaking against the land mass. In general, shorelines with long promontories and gradually sloping underwater shelves extending far out to sea induce waves to break well offshore, minimizing potential wave damage. By contrast, shorelines that slope steeply into the sea with little offshore hindrance to water movement can magnify the violence of waves breaking on the shore. Considerations of protection from damaging waves are similar to those of exposure to winds, and figured in the placement of harbors in the Bronze Age.

The combination of intense weather events, northerly winds, waves, topography, and swift current flow with complex patterns of eddies affecting the western coast of the Aegean is implicated in many shipwrecks in recorded history. Perhaps the most famous of these befell the Persian fleet in three separate incidents during invasions of Greece in the early fifth century BC. In 492, Darius's fleet under Mardonius was wrecked by a northerly gale while rounding the Athos peninsula (Herodotus 6.44). Many of these ships were battered against the rocky peninsula. Later, Xerxes' fleet suffered two major shipwrecks in the summer of 480 BC. The first of these occurred on the long and nearly harborless Magnesia coast near Artemision/Cape Sepias (Herodotus 7.188—92). There, a great four-day storm driven by meltemi winds from the northeast roiled the sea in high waves, sinking ships caught in the open sea and dashing others onto the rocks along the rugged coastline. Remarkably, Herodotus records that locals called these storms “Hellespontian" (i. e., originating in the Dardanelles). The third disaster took place while the fleet was sailing off the “Hollows of Euboea," that is, the eastern coast of the southern half of Euboea, before entering the Doro Channel (Herodotus 8.12—13). In that event, a violent storm driven by northerly winds rose at night and dashed ships against the coastal rocks. These calamities present a characteristically Aegean cocktail of hazards: violent squalls and heavy seas that arise at night, forced by high northerly winds and swift, shifting coastal currents, driving ships toward nearly invisible rocks and shoals on a rugged coastline with few opportunities for safe anchorage. The Persian shipwrecks also illustrate the way that phenomena at all scales, from global to local, interact to produce conditions experienced at human scale.

Aegean Variability

By virtue of its geographical position — a long north to south axis closed in on the north by the land masses of Greece, Anatolia, and the Balkans, and in the south opening into the broad eastern Mediterranean — as well as a complex topography, the Aegean Sea creates a unique maritime environment. The environmental forces that drive atmospheric and hydrospheric circulation converge and cross-cut the Aegean basin in such a way that local conditions, resulting from the interaction of forces operating at all scales, are highly diverse and changeable. The greatest differences are evident as one moves from north to south, through successive influences of continental, Mediterranean, and desert climatic zones, but significant contrasts also occur between the mainland and islands, as well as between contrasting topographic settings regardless of geographical location. Furthermore, seasonal patterns in environmental conditions give a very different character to a given coastal setting through the year. A brief survey of atmospheric conditions in the Aegean, and an example of seasonal variation at a single Aegean port, will highlight some of these contrasts.