Regio Patalis is Latin for "the Region of Patala". It took its name from the ancient city of Patala (now Thatta) at the mouth of the Indus River.
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.
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”.
Siltation has caused the Indus to change its course many times since the days of Alexander the Great, and the site of ancient Patala has been subject to much conjecture. Ahmad Hasan Dani, director of the Taxila Institute of Asian Civilisations, Islamabad, concluded: “There has been a vain attempt to identify the city of Patala. If ‘Patala’ is not taken as a proper name but only refers to a city, it can be corrected to ‘Pattana’, that is, [Sanskrit for] a city or port city par excellence, a term applied in a later period to Thatta [onetime capital of Sindh], which is ideally situated in the way the Greek historians describe”.