According to Strabo, the Greco-Bactrians seem to have had contacts with China through the silk road trade routes (Strabo, XI.XI.I). Indian sources also maintain religious contact between Buddhist monks and the Greeks, and some Greco-Bactrians did convert to Buddhism. Demetrius, son and successor of Euthydemus, invaded north-western India in 180 BC, after the destruction of the Mauryan empire there; the Mauryans were probably allies of the Bactrians (and Seleucids). The exact justification for the invasion remains unclear, but by about 175 BC, the Greeks ruled over parts of north-western India. This period also marks the beginning of the obfuscation of Greco-Bactrian history. Demetrius possibly died about 180 BC; numismatic evidence suggest the existence of several other kings shortly thereafter. It is probable that at this point that the Greco-Bactrian kingdom split into several semi-independent regions for some years, often warring amongst themselves. Heliocles was the last Greek to clearly rule Bactria, his power collapsing in the face of central Asian tribal invasions (Scythian and Yuezhi), by about 130 BCE. However, Greek urban civilisation seems to have continued in Bactria after the fall of the kingdom, having a hellenising effect on the tribes which had displaced Greek-rule. The Kushan empire which followed continued to use Greek on their coinage and Greeks continued being influential in the empire.