§ 218. Belligerents on occasions arrange between themselves that passports and safe-conducts shall be given to certain of each other's subjects. Passports are written permissions given by a belligerent to enemy subjects, or others, allowing them to travel within that belligerent's territory or enemy territory occupied by him. Safe-conducts are written permissions given by a belligerent to enemy subjects, or others, allowing them to proceed to a particular place for a defined object, for instance, to a besieged town for conducting certain negotiations; but safe-conducts may also be given for goods, and they then comprise permission to carry such goods without molestation to a certain place. Passports as well as safe-conducts make the grantee inviolable so long and in so far as he complies with the conditions specially imposed upon him or made necessary by the circumstances of the special case. Passports and safe-conducts are not transferable, and they may be granted to enemy subjects for a limited or an unlimited period; in the former case their validity ceases with the expiration of the period. Both may be withdrawn, not only when the grantee abuses the protection, but also for military expediency. It must, however, be specially observed that passports and safe-conducts are only a matter of International Law when the granting of them has been arranged between the belligerents or their responsible commanders, or between belligerents and neutral Powers. If they are granted without such an arrangement, unilaterally on the part of one of the belligerents, they fall outside the scope of International Law.[434] [Footnote 434: The distinction between passports and the like arranged between the belligerents to be granted, on the one hand, and, on the other, such as are granted unilaterally, would seem to be necessary, although it is not generally made.] [Sidenote: Safeguards.]