Rome's economy relied chiefly on agriculture and war: farming sustained the populace while military campaigns generated necessary funds for various other needs. The soldiers used in these campaigns were farmers who were kept in the army for longer and longer periods of time as Rome expanded in conquest. The story of Spartacus has been told by historians, novelists, and filmmakers up to the present day when it enjoys a wide following as a very popular television series but admiration for the hero of the Third Servile War is nothing new. Karl Marx once noted in a letter to Engels that Spartacus was among the greatest, if not the greatest, hero of the ancient world and held him up as an example to be followed (Volume 41, 265). Stanley Kubrick's famous 1960 film Spartacus, based on the Howard Fast novel, portrayed him as a freedom fighter leading his people against the oppressive system of Roman slavery and every portrayal of the rebel gladiator which has come after Kubrick's film has followed suit to greater or lesser degrees.