Complex sentence: Upon Benedetto's return from England, there is an eight-year period in which nothing is known about his life, after which Benedetto was sent to France to supervise the collection of a tithe in 1276 and then became a papal notary in the late 1270s.
Split into simpler sentences: Upon Benedetto's return from England, there is an eight year period in which nothing is known about what occurred in his life. After this eight year period of uncertainty, Benedetto was sent to France to supervise the collection of a tithe in 1276 and then became a papal notary in the late 1270s.