States and rulers have always regarded the ability to determine who enters or remains in their territories as a key test of their sovereignty, but prior to World War I, border controls were only sporadically implemented.[2] In medieval Europe, for example, the boundaries between rival countries and centres of power were largely symbolic or consisted of amorphous borderlands, ‘marches’ and ‘debatable lands’ of indeterminate or contested status and the real ‘borders’ consisted of the fortified walls that surrounded towns and cities, where the authorities could exclude undesirable or incompatible people at the gates, from vagrants, beggars and the ‘wandering poor’, to ‘masterless women’, lepers, Gypsies or Jews.[3]