What documents would historians study in order to understand the gap in the bridge

Historians would study magazine, research paper, survey reports in order to understand the gap in the bridge.

Explanation:

Historian and archaeologist study the past and the contemporary issues also. For that they culture historical documents, evidences and reports, memoirs etc. Past is the key of the present. There is always an interconnection in between past and present situation.

To understand the gap in the bridge magazines, primary survey reports, research article, gazetteers help a lot. Empirical research means practical visit to a place or experiment of gathered information for its validity expedition is also done by the historians.