Wikipedia
Indo-Scythians is a term used to refer to Scythians ( Sakas), who migrated into parts of central and northern South Asia ( Sogdiana, Bactria, Arachosia, Gandhara, Sindh, Kashmir, Punjab, Haryana, Rajasthan,...), from the middle of the 2nd century BC to the 4th century AD.
The first Saka king in south Asia was Maues (Moga) (1st century BC) who established Saka power in Gandhara (modern day Pakistan and Afghanistan region) and gradually extended supremacy over north-western India. Indo-Scythian rule in northwestern India ended with the last Western Satrap Rudrasimha III in 395 CE who was defeated by the Indian Emperor Chandragupta II of the Gupta Empire. The power of the Saka rulers started to decline in the 2nd century CE after the Indo-Scythians were defeated by the south Indian Emperor Gautamiputra Satakarni of the Satavahana dynasty. Later the Saka kingdom was completely destroyed by Chandragupta II of the Gupta Empire in the 4th century.
The invasion of India by Scythian tribes from Central Asia, often referred to as the Indo-Scythian invasion, played a significant part in the history of South Asia as well as nearby countries. In fact, the Indo-Scythian war is just one chapter in the events triggered by the nomadic flight of Central Asians from conflict with tribe such as the Xiongnu in the 2nd century AD, which had lasting effects on Bactria, Kabul, and India as well as far-off Rome in the west, and more nearby to the west in Parthia.
It has been claimed that ancient Roman historians including Arrian and Claudius Ptolemy have mentioned that the ancient Sakas ('Sakai') were basically nomads. However, Italo Ronca, in his detailed study of Ptolemy's chapter vi, marks the statement: "The land of the Sakai belongs to nomads, they have no towns but dwell in forests and caves" as spurious.