According to Eratosthenes a century later, latitudinal zones around the earth were considered to be associated with a particular type of climate—torrid, temperate and frigid. In late antiquity (from the third to early seventh century AD), it was believed that the habitable world encompassed seven climates (associated with the seven planets by astrological writers). The climatic zones were named after the places where they crossed the meridian of Alexandria in Egypt. Their central lines passed respectively through Meroe (200 km northeast of Khartoum), Aswan, Alexandria, Rhodes, the Hellespont (or Rome), the mouth of the Dnieper River and either ‘Thule’ or the Ural Mountains. A more comprehensive system divided the northern and southern hemispheres into 24 climates, each corresponding to an increase in day length of the longest day of 30 min (Oxford English Dictionary online, 2011).