I believe that by the time of the Gracchi most of the existing ager publicus in the ager Romanus had been given private rights of tenure, making it either ager quaestorius (land auctioned by the quaestors in Rome), ager censorius (land leased out by the censors for a rent) and ager in trientabulis (land given as repayment to Roman creditors during the Second Punic War); the most convincing recent interpretation of the lex Sempronia that I have read actually cites the law itself as the reason for the conversion of most of the former ager publicus into private land, since Tiberius' law made hereditary possession of ager publicus within the 500 iugera limitation permanent and tried to offer private rights of tenure to everyone intended to be covered under his law. With the Gracchan land commission no more by the last decade of the second century, the lex Thoria of 111 was essentially the logical end of distributing ager publicus with no history of Roman settlement. The agrarian movements of the first century were similar in intention but quite different in nature to the lex Sempronia.