16 And this concord between civilized nations is maintained ant fostered by the modern custom of visits and meetings at which the Heads of States and Princes are accustomed to treat of matters of special importance. So then, considering the changed circumstances of the times and the dangerous trend of events, and in order to encourage this concord, We would not be unwilling to relax in some measure the severity of the conditions justly laid down by Our Predecessors, when the civil power of the Apostolic See was overthrown, against the official visits of the Heads of Catholic states to Rome. But at the same time We formally declare that this concession, which seems counselled or rather demanded by the grave circumstances in which to-day society is placed, must not be interpreted as a tacit renunciation of its sacrosanct rights by the Apostolic See, as it is acquiesced in the unlawful situation in which it is placed. Rather do we seize this opportunity to renew for the same reasons the protests which Our Predecessors have several times made, not in the least moved thereto by human interests, but in fulfilment of the sacred duty of their charge to defend the rights and dignity of this Apostolic See; once again demanding, and with even greater insistence now that peace is made among the nations that "for the Head of the Church, too, an end may be put to that abnormal condition which in so may ways does such serious harm to tranquillity among the peoples."
Source: Pacem, Dei Munus Pulcherrimum (Vatican.va)