Question

what kind of evidence is the historians case to find out about trade relation

Answer 1

A historian can find the trade relation of an ancient civilization by analyzing the proofs presented in literature, analyzing the routes of trade, analyzing the artifacts like pottery, plates, sculptures and more, wrecked ships and old sea routes.

Analyzing the ancient coins can also give a deeper insight about the trade and traders of the civilization. Apart from the coins, artifacts and trade routes, historians consider a document that written for trade commitment as "a lucky shot". Because primary documents like signed parchments, papers, photographs are some significant source to decipher an event that once actually took place.