Answer: Written documents
Explanation: Written documents are the most reliable source of information about an event or period for any historian. This means written documents found in historical archives, or in any way known as reliable sources, may not always be found in archives. It is understood that these written documents provide valid and convincing evidence of their veracity and credibility. However, for example, when looking for historical sources about a period when there was no written evidence, such as in the time of Homo Sapiens, information about that period can also be sought with drawings or some art on the walls, etc.
