Answer:
Explanation:
They did this because they wanted to convert them to Islam's religion and to trade. they probably wrote stories and the people that study them probably found them. :)
Answer: Quite a few things
Explanation: Well, traders leave their marks on civilization quite easily. Due to their goods being thrown around in the area the stories of their travels will become known quite quickly.
As for why did they come so far? Quite a few things, one would to be spreading their religion, and the other would be to offer goods and services to people without those tools for a higher profit
