Question

how are the accounts of foreign travellers useful to historians

Answer 1

Foreign travellers normally examine things from a perspective of neutrality and generally make observations as they see at the time of the visit, not having any preconceived notions. They come from a different culture and environment, hence historians trust their accounts to be nearest to the truth.  

Answer 2

Accounts of foreign travellers or travelogues are helpful to historians as they have given detailed account of political events about trade and commerce etc.Foreign travellers no.rmally examine things from a perspective of neutrality and generally make observations as they see at the time of the visit, not having any preconceived notions. They come from a different culture and environment, hence historians trust their accounts to be nearest to the truth.