Medieval economic and social historians are accustomed to dealing in long periods of time: often in centuries rather than decades. Indeed, it has long proved seductive to divide the half millennium from the Norman Conquest to the accession of the Tudors into just two parts: the first, running from the late eleventh century to the early fourteenth - the 'long thirteenth century' - characterised by expansion, urbanisation, commercialisation and, eventually, overpopulation; the second - 'the long fifteenth century' - characterised by retreat and retrenchment. By common consensus, tendencies developed in the first era which became progressively more favourable to landlords and injurious to the mass of the peasantry, while in that which succeeded it these tendencies were thrown into reverse, with the result that the mass of the people benefited at the expense of their social and economic superiors.