Cyrus (558-530BC) of Persia was the first conqueror who penetrated into Indian subcontinent. He destroyed the city of Capisa (north of Kabul). Herodotus the Greek Historian tells us that in 516 BC Darius I (552-486BC) sent a naval expedition to explore the valley of the Sindhu River and annexed the part of Punjab and Sind. The main impact of Persian invasion was the introduction of the Aramaic form of writing which later developed into the Kharosti alphabet. It led to promotion and increase in Indo- Iranian trade. The fusion of Iranian and Persian features into the Mauryan art was visible. Buddhism impacted the Zoroastrian religion of ancient Persia.
After the conquest of the Persian Empire, Alexander marched to India through the Khyber Pass in 326 BC. He constructed a bridge and proceeded towards Taxila.The King of Taxila surrendered and offered to help Alexander. The most powerful among the North Western was the ruler of Kingdom between Hydaspes (Jhelum) and the Acesines (Chenab) whom the Greeks call Porus.Porus was defeated and made captive by Alexander. Alexander’s advance was arrested on the bank of the Beas for his soldiers mutinied and refused to proceed further after the battle of Vitasta and Jhelum. While retreating he divided the whole territory from the Indus to the Beas into three provinces and put them under the overall charge of three Greek governors. The Greek invasion of India opened the trade route between northwest India and west Asia. The invasion led to more Greek settlements in this area. Opening up of four distinct routes between India and Greek by land and sea paved the way for increased trade and cultural contacts between the two regions. Indians learnt from the Greek in the fields of astronomy, coinage, architecture and sculpture. The Gandhara school of Sculpture became well known.