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. 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.