A title borrowed from the final division of the Roman legion (the *decaneus* was the commander of ten soldiers) and later from monastic rules, especially the Rule of St Benedict (ch. 21), from the mid-9th century the title was given in many cathedral chapters to a dignity, often identical with that of archpriest (*decanus capituli*). It is also the name given to the official placed over a grouping of rural parishes, now called the rural vicar (*vicario foraneo*), a kind of intermediate organ between the parish priests and the bishop, and from the late 9th century between the parish priests and the archdeacon (*decanus* i.e. *archipresbyter parochiarum*).
To the first was entrusted the care of the chapter for internal affairs and the divine service; to the second fell a certain jurisdiction over the clergy and churches of his own territory (v. ARCHPRIEST; CHAPTER; RURAL VICAR).
In chapters the dean or archpriest in the 11th–12th centuries existed in almost every diocese, was ordained priest for the cure of souls entrusted to him (c. 7, § 2, X, de elect. I, 6; c. 1 et seq., D. 60), but by common law was subject to the archdeacon (c. 7, § 2, 3, X, de off. arch., I, 23; c. 1, X, de off. archipresb. I, 24). Sometimes the dean was the same as the archpriest; in some chapters he was a distinct dignity, in others he became the first dignity, while in others still the name was given to the senior canon without forming a true dignity. This situation has persisted even in current law, where in any given chapter according to its own statutes different cases may arise: in Spain, for example, the dean is the first dignity, in Bavaria the second; in many chapters he does not exist as a separate dignity but is the senior canon by appointment.
In parochial districts the office of dean, which had become common in the 11th–12th centuries, underwent various developments. Today the rural vicar is called dean (sometimes *decanus ruralis*) when his district, by particular law, has retained the name *decanatus* (cf. can. 217, § 1).
Moreover, in the 1917 Code of Canon Law (*CIC*), in a generic sense, dean is he who, among those belonging to the same grade of the hierarchy of jurisdiction, in any college or moral body, is the first promoted to that grade, or, at equal grade, the senior by ordination, and finally, at equal date of ordination, the senior by age.
To him, as dean, no power of jurisdiction pertains of himself (cann. 237 § 1, 1598 § 1), unless by prescription of law he succeeds to another’s power (cann. 309 § 4, 432 § 1, 434 § 3) or has particular tasks entrusted to him (cf. can. 429 § 5); but he does have the right of precedence (can. 106, n. 3), to which, often in the absence of other authority, is added the right to preside (can. 284, n. 2) or to convoke the college, determining, if necessary, the place of meeting (can. 284, 289 § 1, 397 n. 4).
Two colleges in the 1917 *CIC* have an actual office of dean with particular duties and privileges: the college of cardinals (v. § 2; const. *Vacante Sede Apost.*, c. II, n. 8, III, nn. 50, 51, 52, 54, VII 100, 106), where the dean is the cardinal-bishop of most senior creation, who as such holds the title of bishop of Ostia; and the college of Auditors of the Sacred Roman Rota (v. ROTA), in which the dean is the senior auditor by number (can. 1598 § 1). In both colleges the dean becomes such *ipso iure* by seniority and is *primus inter pares*.
In the papal chapel and household (v.) besides the dean of the chamber, there are frequent colleges presided over by a dean (the college of protonotaries *de numero* attached to the Apostolic Camera, the college of prelates-clerics of the Apostolic Camera, the college of voting prelates of the Apostolic Signatura, the college of advocates of the Sacred Conclave, the college of procurators of the Sacred Apostolic Palaces, the college of clerics of the papal chapel, the college of masters of ceremonies of the Virga Rubea, the college of papal mace-bearers and couriers).
In ecclesiastical universities too there exists the office of dean, one of the academic authorities, dean of a faculty (Apostolic Constitution *Deus scientiarum Dominus* of Pius XI, tit. II, arts. 15, 17), whose duties are defined by the Ordinations of the Sacred Congregation of Seminaries and Universities of Studies of 12 June 1931 (art. 7). Unlike other colleges and moral bodies, here the deanship is generally an elective office with a certain power of jurisdiction.