A corner of the exhibition hall where the two letters are on display.[Photo/Sipa]

The artifacts provide an insight into social development during that period. According to experts' research, in all probability the letters were delivered home by the brothers' acquaintances since personal letters were not permitted to be conveyed through the official postal service until the Song Dynasty (960-1279).

People today can learn about the letter writing conventions during the period of the artifacts. One of the differences found by scholars was the way the date was written at the beginning of the letter rather than at the end, as is currently practiced. Researchers also noted that some words used in the letters are still part of today's Chinese vocabulary.