The biography of every compiler in this group reads the same way: born in one province, then years of travel through Iraq, Arabia, Syria, Egypt and Iran, sitting with one teacher after another. That travel was not incidental. It was the method, and it had a technical justification. A report reaches you through a chain of transmitters, and every additional link is another point at which error can enter, so a scholar who hears a report from an old man who heard it from a companion has a shorter and better chain than one who receives the same words through four intermediaries. A high chain, meaning a short one, was worth a journey of a thousand miles, and scholars said so plainly.
The consequences run in two directions. It built a genuine international network, in which a student trained in Iran could be examined in Egypt on material collected in Basra and everyone involved knew the standards being applied, which is a remarkable intellectual infrastructure for the ninth century. It also created pressure. A traveller who has crossed a continent to hear an aged authority has an interest in the value of what he receives, and the critical literature on transmitters, which records who was careless, who confused his sources late in life and who was suspected of inventing, exists because the discipline was aware of the problem it had created for itself.