It seems certain that in the twelfth century vicars were named only when the pope absented himself for a long time from Rome or its neighbourhood. When he returned, the vicar's duties ceased. This may have lasted to the pontificate of Pope Innocent IV (1243–54); on the other hand it is certain that in the latter half of the thirteenth century the vicar continued to exercise the duties of his office even during the presence of the pope at Rome. Thus the nomination of a vicar on 28 April 1299, is dated from the Lateran. The office owes its full development to the removal of the Roman Curia to Southern France and its final settlement at Avignon. Since then the list of vicars is continuous.
The oldest commissions do not specify any period of duration; in the Bull of 16 June 1307, it is said for the first time that the office is held "at our good will". It is only in the sixteenth century that we meet with life-tenures; the exact year of this important modification remains yet to be fixed. Formerly the nomination was by Bull; when began the custom of nominating by Brief is difficult to determine. The oldest Bull of nomination known bears the date of 13 February 1264.
An immemorial custom of the Curia demands that all its officials shall be duly sworn in, and this was the case with the vicars. In all probability during the twelfth and thirteenth centuries such oaths were taken at the hands of the pope himself. Later the duty fell to the Apostolic Camera. The oath, whose text (though very much older) first appears in a document of 21 May 1427, greatly resembles, in its first part, the usual episcopal oath; while the latter part applies to the office in question. The oath is conceived in very general terms and lays but slight stress on the special duties of the vicar. The official named on 18 October 1412, as representative of the vicar was also sworn in, and before entering on his office was admonished to take, in presence of a specified cardinal, the usual oath of fidelity to the pope and of a faithful exercise of the office.