Regio Patalis is Latin for “the region of Patala”, that is the region around the ancient city of Patala at the mouth of the Indus River in Sindh, Pakistan. The historians of Alexander the Great state that the Indus parted into two branches at the city of Patala before reaching the sea, and the island thus formed was called Patalene, the district of Patala. Alexander constructed a harbour at Patala. While the Patala was well known to mariners and traders of the Ancient Mediterranean, by the European Middle Ages, mapmakers no longer knew its location. Regio Patalis appeared on late 15th and early 16th century maps and globes in a variety of increasingly erroneous locations, further and further east and south of India. It even appeared on some maps as a promontory of Terra Australis. The Regio Patalis in classical literature Pliny the Elder (Gaius Plinius Secundus, 23-79 AD) referring to “the island of Patale, at the mouth of the Indus”, wrote in Historia Naturalis: “Also in India [as well as at Aswan in Egypt] at the well-known port of Patale the sun rises on the right and shadows fall southward”. The geographer Strabo (c.64 BC–c.24 AD) had said: “The Indus falls into the southern sea by two mouths, encompassing the country of Patalênê, which resembles the Delta in Egypt”. He noted: “All these [nations] were conquered by Alexander, and last of all he reduced Patalênê, which the Indus forms by splitting into two branches… Patalênê contains a considerable city, Patala, which gives its name to the island”. The 1507 Martin Waldseemüller map shows Patala in this location. In the late 2nd century BC, Agatharchides of Cnidus recorded merchants from Patala, or as he called it, Potana, coming to the island of Socotra to trade with Alexandrian merchants. The 2nd century AD author Dionysios Periegetes said in his Orbis Descriptio: “This river [the Indus] has two mouths, and dashes against the island enclosed between them, called in the tongue of the natives, Patalênê”. Or, as Priscian put it in his popular rendition of Periegetes: “the River Indus... Patalene is girt by its divided waters.” Some scholars identify Patala with Thatta, a one-time capital of Sindh. But the identity of Patala is much debated among scholars. However, as 'Regio' is Latin for 'region', one might expect that 'Patalis' may also be of Latin origin. This indeed appears to be the case,