Since the beginning of time, and as a natural instinct, foreigners are usually treated as invaders and were not welcome into one's home, in the Middle Ages a 'foreigner' meant not only anyone who arrived from outside one's town or village, but potentially an enemy and those without legal status. Foreigners were without legal rights until they paid a surety, this circumstance was dealt with by the courts of law and there many various regulations setting fees for running a business or renting a house.
Foreigners without legal status were not allowed to acquire or inherit ownership, and were still not as welcome as one would think even with the payment of surety, they would sometimes carry possible diseases which would endanger the whole land if not properly treated, thus great caution was taken when permitting immigrants.