Their original purpose was the enrolment of Letters Close (i.e. letters sealed closed) issued under the Great Seal, which typically conveyed orders to the officers of the crown; these included writs summoning peers to Parliament. Enrolments declined as the use of the Great Seal was supplanted by that of the Privy Seal, and ceased altogether during the reign of Henry VIII. The Close Rolls were also used for the enrolment of private deeds; particularly after many were destroyed in the Peasants' Revolt. (medievalgenealogy.org)