The History of the Indo-Greek Kingdom covers a period from the 2nd century BCE to the beginning of the 1st century CE in northern and northwestern India. There were over 30 Indo-Greek kings, often in competition on different territories. Many of them are only known through their coins. Many of the dates, territories, and relationships between Indo-Greek kings are tentative and essentially based on numismatic analysis (find places, overstrikes, monograms, metallurgy, styles), a few Classical writings, and Indian writings and epigraphic evidence. The following list of kings, dates and territories after the reign of Demetrius is derived from the latest and most extensive analysis on the subject, by Osmund Bopearachchi and R. C. Senior. The invasion of northern India, and the establishment of what would be known as the "Indo-Greek kingdom", started around 200 BCE when Demetrius, son of the Greco-Bactrian king Euthydemus I, led his troops across the Hindu Kush. Apollodotus, may have made advances in the south, while Menander, led later invasions further east. Following his conquests, Demetrius received the title ανικητος ("Anicetus", lit. invincible), a title never given to any king before. Written evidence of the initial Greek invasion survives in the Greek writings of Strabo and Justin, and in Sanskrit in the records of Patanjali, Kālidāsa, and in the Yuga Purana, among others. Coins and architectural evidence also attest to the extent of the initial Greek campaign. Evidence of the initial invasion Greco-Roman sources The Greco-Bactrians went over the Hindu Kush and also started to re-occupy the area of Arachosia, where Greek populations had been living since before the acquisition of the territory by Chandragupta from Seleucus. Isidore of Charax describes Greek cities there, one of them called Demetrias, probably in honour of the conqueror Demetrius. According to Strabo, Greek advances temporarily went as far as the Shunga capital Pataliputra (today Patna) in eastern India: The 1st century BCE Greek historian Apollodorus, quoted by Strabo, affirms that the Bactrian Greeks, led by Demetrius I and Menander, conquered India and occupied a larger territory than the Greeks under Alexander the Great, going beyond the Hypanis towards the Himalayas: The Roman historian Justin also mentioned the Indo-Greek kingdom, describing a "Demetrius, King of the Indians" ("Regis Indorum"), and explaining that after vanquishing him Eucratides in turn "put India under his rule" ("Indiam in potestatem redegit") (since the time of the embassies of Megasthenes in the 3rd century BCE