Date | Country | Change |
| 402 |  Scotland | Diocese of Whithorn was established |
| 410 |  Iraq | Diocese of Perat-Maishan (Chaldean Rite) was promoted as Metropolitan Archdiocese of Perat-Maishan |
| 417 |  France | Diocese of Arles was promoted as Metropolitan Archdiocese of Arles (with suffragan sees Antibes, Cavaillon, Marseille, Orange and Saint-Paul-Trois-Châteaux) |
| 420 |  Algeria | Diocese of Jomnium was suppressed |
| 421 | France | Diocese of Lodève was established |
| 439 |  Ireland | Abbacy nullius of Dunshaughlin was established |
| 439 |  Italy | Diocese of Galazia in Campania was established |
| 440 | France | Diocese of Uzès was established (from Diocese of Nîmes and became suffragan of Arles) |
| 440 | Ireland | Abbacy nullius of Ardmore was established |
| 440 | Ireland | Abbacy nullius of Killala was established |
| 440 | Italy | Diocese of Ivrea was established (became suffragan of Milano) |
| 440 | Italy | Diocese of Ravenna was promoted as Metropolitan Archdiocese of Ravenna (with suffragan sees Faenza, Forlì, Imola, Modena and Voghenza) |
| 440 |  Portugal | Diocese of Braga was promoted as Metropolitan Archdiocese of Braga (with suffragan see Astorga) |
| 445 | France | Diocese of Narbonne was promoted as Metropolitan Archdiocese of Narbonne (with suffragan sees Béziers, Lodève, Nîmes and Toulouse) |
| 445 | France | Diocese of Vienne was promoted as Metropolitan Archdiocese of Vienne (with suffragan sees Die, Toulon and Viviers) |
| 445 |  Northern Ireland, Ireland | Archdiocese of Armagh was established |
| 449 |  Spain | Diocese of Tarazona was established |
| 450 | Algeria | Diocese of Hippo Regius was suppressed |
| 450 |  Belgium | Diocese of Tournai was established (from Metropolitan Archdiocese of Reims and became suffragan of Reims) |
| 450 | France | Diocese of Le Mans was established (became suffragan of Tours) |
| 450 | France | Diocese of Senez was established |
| 450 | France | Diocese of Tours was promoted as Metropolitan Archdiocese of Tours (with suffragan sees Angers, Le Mans, Nantes, Rennes and Vannes) |
| 450 | France | Diocese of Vannes was established (became suffragan of Tours) |
| 450 | Ireland | Abbacy nullius of Ardagh was established |
| 450 | Ireland | Abbacy nullius of Duleek was established |
| 450 | Ireland | Abbacy nullius of Elphin was established |
| 450 | Ireland | Abbacy nullius of Killashee was established |
| 450 | Italy | Diocese of Amelia was established |
| 450 | Italy | Diocese of Aquaviva was established |
| 450 | Italy | Diocese of Aquino was established |
| 450 | Italy | Diocese of Aveia Vestina was established |
| 450 | Italy | Diocese of Camerino was established |
| 450 | Italy | Diocese of Carmeiano was established |
| 450 | Italy | Diocese of Città di Castello was established (without ecclesiastical province) |
| 450 | Italy | Diocese of Cremona was established (became suffragan of Milano) |
| 450 | Italy | Diocese of Cuma was established |
| 450 | Italy | Diocese of Faleri was established |
| 450 | Italy | Diocese of Falerone was established |
| 450 | Italy | Diocese of Forum claudii was established |
| 450 | Italy | Diocese of Gabi was established |
| 450 | Italy | Diocese of Gualdo Tadino was established |
| 450 | Italy | Diocese of Labico was suppressed (to establish Diocese of Subaugusta) |
| 450 | Italy | Diocese of Montecassino was established |
| 450 | Italy | Diocese of Ofena was established |
| 450 | Italy | Diocese of Reggio Emilia was established (became suffragan of Milano) |
| 450 | Italy | Diocese of Salpi was established |
| 450 | Italy | Diocese of Sant’Angelo in Vado was established |
| 450 | Italy | Diocese of Subaugusta was established (from Papal See of Roma and from the suppressed Diocese of Labico) |
| 450 | Italy | Diocese of Sulmona was established |
| 450 | Italy | Diocese of Sutri was established |
| 450 | Italy | Diocese of Tarquinia was established |
| 450 | Italy | Diocese of Tronto was established |
| 450 | Italy | Diocese of Valva was established |
| 450 | Italy | Diocese of Velletri was established (became suffragan of Roma) |
| 450 |  Jordan | Diocese of Neila was established |
| 450 | Northern Ireland | Abbacy nullius of Down was established |
| 450 | Spain | Diocese of Egara was established (from Diocese of Barcelona) |
| 450 | Spain | Diocese of Ibiza was established |
| 450 | Spain | Diocese of Mallorca was established |
| 450 |  Tunisia | Diocese of Garriana was established |
| 450 |  Turkiye | Diocese of Hierapolis was promoted as Metropolitan Archdiocese of Hierapolis |
| 451 |  Egypt | Diocese of Alexandria was promoted as Patriarchal See of Alexandria |
| 451 | Italy | Diocese of Vibo Valentia was established |
| 451 |  Palestine,  Cyprus,  Israel, Jordan | Diocese of Jerusalem was promoted as Patriarchal See of Jerusalem |
| 451 | Turkiye | Metropolitan Archdiocese of Constantinople was promoted as Patriarchal See of Constantinople |
| 454 | Ireland, Northern Ireland | Abbacy nullius of Clogher was established |
| 457 | Italy | Diocese of Blera was established |
| 460 | Italy | Diocese of Telese was established |
| 463 | Spain | Diocese of Calahorra was established |
| 465 | France | Diocese of Cimiez was suppressed (to Diocese of Nice) |
| 465 | Italy | Diocese of Luni was established |
| 465 | Italy | Diocese of Numana was established |
| 465 | Italy | Diocese of Passo Corese was established |
| 468 | Portugal | Diocese of Coinimbriga was renamed as Diocese of Aeminium |
| 470 | France | Diocese of Rodez was established (became suffragan of Bourges) |
| 470 | Spain | Diocese of Tarragona was promoted as Metropolitan Archdiocese of Tarragona (with suffragan sees Auca, Calahorra, Gerona and Tarazona) |
| 480 | Italy | Diocese of Anagni was established (without ecclesiastical province) |
| 480 | Italy | Diocese of Fano was established |
| 480 | Italy | Diocese of Ferentino was established (without ecclesiastical province) |
| 480 | Italy | Diocese of Foligno was established (without ecclesiastical province) |
| 480 | Italy | Diocese of Lorium was established |
| 480 | Italy | Diocese of Venafro was established |
| 482 |  Austria | Diocese of Juvavo was suppressed |
| 484 | Italy | Diocese of Cagliari was promoted as Metropolitan Archdiocese of Cagliari (with suffragan sees Tharros and Torres) |
| 484 | Italy | Diocese of Forum Traiani was established |
| 484 | Italy | Diocese of Sulci was established |
| 490 | Ireland | Abbacy nullius of Kildare was established |
| 490 | Italy | Diocese of Alife was established |
| 490 | Italy | Diocese of Arna was established |
| 490 | Italy | Diocese of Avellino was established |
| 490 | Italy | Diocese of Bolsena was established |
| 490 | Italy | Diocese of Chieti was established |
| 490 | Italy | Diocese of Minturno was established |
| 490 | Italy | Diocese of Norcia was established |
| 490 | Italy | Diocese of Perugia was established |
| 490 | Italy | Diocese of Populonia was established |
| 490 | Italy | Diocese of Potenza was established |
| 490 | Italy | Diocese of Roselle was established |
| 490 | Italy | Diocese of Salerno was established |
| 490 | Italy | Diocese of Segni was established |
| 490 | Italy | Diocese of Sessa Aurunca was established |
| 490 | Italy | Diocese of Sorrento was established |
| 490 | Italy | Diocese of Taranto was established |
| 498 | Italy | Diocese of Tindari was established |
| 499 | France | Diocese of Arras was established (from Metropolitan Archdiocese of Reims and became suffragan of Reims) |
| 499 | Italy | Diocese of Cerveteri was established |
| 500 |  Albania | Diocese of Apollonia was suppressed |
| 500 | Albania | Diocese of Lestrona was suppressed |
| 500 | Algeria | Diocese of Bagai was suppressed |
| 500 | Algeria | Diocese of Calama was suppressed |
| 500 | Algeria | Diocese of Gegi was suppressed |
| 500 | Algeria | Diocese of Icosium was suppressed |
| 500 | Algeria | Diocese of Midila was suppressed |
| 500 | Algeria | Diocese of Rusguniæ was suppressed |
| 500 | Algeria | Diocese of Thagaste was suppressed |
| 500 | Algeria | Diocese of Tubunæ was suppressed |
| 500 | Austria | Diocese of Aguntum was established |
| 500 | Austria | Metropolitan Archdiocese of Lauriacum was suppressed |
| 500 |  Bosnia and Herzegovina | Diocese of Bistue was established |
| 500 |  Croatia | Diocese of Salona was promoted as Metropolitan Archdiocese of Salona (with suffragan sees Ragusa and Zadar) |
| 500 | Croatia | Diocese of Vinkovci was suppressed |
| 500 | Egypt | Diocese of Nilopolis was suppressed |
| 500 | France | Diocese of Agde was established (from Diocese of Nîmes and became suffragan of Narbonne) |
| 500 | France | Diocese of Aix was promoted as Metropolitan Archdiocese of Aix (with suffragan sees Apt, Fréjus, Gap, Riez and Sisteron) |
| 500 | France | Diocese of Aléria was established |
| 500 | France | Diocese of Avranches was established (became suffragan of Rouen) |
| 500 | France | Diocese of Belley was established (became suffragan of Besançon) |
| 500 | France | Diocese of Briançonnet was established |
| 500 | France | Diocese of Couserans was established (became suffragan of Eauze) |
| 500 | France | Diocese of Coutances was established (became suffragan of Rouen) |
| 500 | France | Diocese of Dax was established (became suffragan of Eauze) |
| 500 | France | Diocese of Glandèves was established |
| 500 | France | Diocese of Javols was suppressed (to establish Diocese of Mende) |
| 500 | France | Diocese of Lectoure was established (became suffragan of Eauze) |
| 500 | France | Diocese of Lescar was established (became suffragan of Eauze) |
| 500 | France | Diocese of Lisieux was established (became suffragan of Rouen) |
| 500 | France | Diocese of Mariana was established |
| 500 | France | Diocese of Meaux was established (became suffragan of Sens) |
| 500 | France | Diocese of Mende was established (from the suppressed Diocese of Javols and became suffragan of Bourges) |
| 500 | France | Diocese of Nebbio was established |
| 500 | France | Diocese of Nevers was established (became suffragan of Sens) |
| 500 | France | Diocese of Oloron was established (became suffragan of Eauze) |
| 500 | France | Diocese of Quimper was established (became suffragan of Tours) |
| 500 | France | Diocese of Rouen was promoted as Metropolitan Archdiocese of Rouen (with suffragan sees Avranches, Bayeux, Coutances, Évreux, Lisieux and Séez) |
| 500 | France | Diocese of Sagone was established |
| 500 | France | Diocese of Saint-Quentin was established (became suffragan of Reims) |
| 500 | France | Diocese of Senlis was established (became suffragan of Reims) |
| 500 | France | Diocese of Séez was established (became suffragan of Rouen) |
| 500 | France | Diocese of Tarbes was established (became suffragan of Eauze) |
| 500 | France | Diocese of Tarentaise was established (became suffragan of Vienne) |
| 500 | France | Diocese of Vernay was suppressed |
| 500 |  Greece | Diocese of Karpathus was established |
| 500 | Greece | Diocese of Patrasso was promoted as Metropolitan Archdiocese of Patrasso |
| 500 | Greece | Diocese of Thespia was suppressed |
| 500 | Iraq | Archdiocese of Kaškar (Chaldean Rite) was suppressed |
| 500 | Ireland | Abbacy nullius of Ardcarne was established |
| 500 | Ireland | Abbacy nullius of Ardfert was established |
| 500 | Ireland, Northern Ireland | Abbacy nullius of Brefinnia was established |
| 500 | Ireland | Abbacy nullius of Connor was established |
| 500 | Ireland | Abbacy nullius of Inniscathy was established |
| 500 | Ireland | Abbacy nullius of Kilfenora was established |
| 500 | Ireland | Abbacy nullius of Louth was established |
| 500 | Ireland | Abbacy nullius of Sléibhte was established |
| 500 | Italy | Diocese of Agropoli was established |
| 500 | Italy | Diocese of Belluno was established |
| 500 | Italy | Diocese of Bevagna was established |
| 500 | Italy | Diocese of Bisenzio was established |
| 500 | Italy | Diocese of Blanda was established |
| 500 | Italy | Diocese of Bovino was established |
| 500 | Italy | Diocese of Bussento was established |
| 500 | Italy | Diocese of Cervia was established (became suffragan of Roma) |
| 500 | Italy | Diocese of Claterna was suppressed (to Diocese of Imola) |
| 500 | Italy | Diocese of Erdonia was suppressed (to Diocese of Eca) |
| 500 | Italy | Diocese of Falerone was suppressed |
| 500 | Italy | Diocese of Fausania was established (became suffragan of Cagliari) |
| 500 | Italy | Diocese of Fidene was established |
| 500 | Italy | Diocese of Foro Flaminii was established |
| 500 | Italy | Diocese of Gallipoli was established |
| 500 | Italy | Diocese of Isernia was established |
| 500 | Italy | Diocese of Labico was restored (from the suppressed Diocese of Subaugusta) |
| 500 | Italy | Diocese of Larino was established |
| 500 | Italy | Diocese of Lipari was established |
| 500 | Italy | Diocese of Locri was established |
| 500 | Italy | Diocese of Meria was established |
| 500 | Italy | Diocese of Messina was established |
| 500 | Italy | Diocese of Miseno was established |
| 500 | Italy | Diocese of Montecassino was suppressed (to Diocese of Aquino) |
| 500 | Italy | Diocese of Ostra was established |
| 500 | Italy | Diocese of Penne was established (without ecclesiastical province) |
| 500 | Italy | Diocese of Pollentia was suppressed (to Diocese of Camerino) |
| 500 | Italy | Diocese of Reggio Calabria was established |
| 500 | Italy | Diocese of Rieti was established (without ecclesiastical province) |
| 500 | Italy | Diocese of Senigallia was established (without ecclesiastical province) |
| 500 | Italy | Diocese of Sepino was established |
| 500 | Italy | Diocese of Spello was established |
| 500 | Italy | Diocese of Subaugusta was suppressed (to establish Diocese of Labico) |
| 500 | Italy | Diocese of Teramo was established (from the suppressed Diocese of Tronto) |
| 500 | Italy | Diocese of Treba was established |
| 500 | Italy | Diocese of Trevi was established |
| 500 | Italy | Diocese of Tronto was suppressed (to establish Diocese of Teramo) |
| 500 | Italy | Diocese of Venosa was established |
| 500 | Jordan | Diocese of Neila was suppressed |
| 500 |  Kosovo | Diocese of Prizren was established |
| 500 |  Libya | Diocese of Sabrata was suppressed |
| 500 | Libya | Diocese of Œa was suppressed |
| 500 |  North Macedonia | Metropolitan Archdiocese of Dardania was suppressed |
| 500 | Portugal | Diocese of Pax Iulia was established (became suffragan of Emerita Augusta) |
| 500 |  Serbia | Diocese of Remesiana was suppressed |
| 500 | Spain | Diocese of Ampurias was established |
| 500 | Spain | Diocese of Coria was established |
| 500 | Spain | Diocese of Iria Flavia was established (became suffragan of Braga) |
| 500 | Spain | Diocese of Lérida was established (became suffragan of Tarragona) |
| 500 | Spain | Diocese of Ourense was established |
| 500 | Spain | Diocese of Pamplona was established (became suffragan of Tarragona) |
| 500 | Spain,  Andorra | Diocese of Urgell was established |
| 500 | Spain | Diocese of Valeria was established |
| 500 | Spain | Diocese of Vergi was established |
| 500 | Spain | Diocese of Vic was established (became suffragan of Tarragona) |
| 500 |  Switzerland | Diocese of Avenches was established (became suffragan of Besançon) |
| 500 | Switzerland | Diocese of Chur was established (became suffragan of Milano) |
| 500 | Tunisia | Diocese of Bennefa was suppressed |
| 500 | Tunisia | Diocese of Garriana was suppressed |
| 500 | Tunisia | Diocese of Menefessi was suppressed |
| 500 | Tunisia | Diocese of Sufes was suppressed |
| 500 | Tunisia | Diocese of Tambeæ was suppressed |
| 500 | Tunisia | Diocese of Theudalis was suppressed |
| 500 | Tunisia | Diocese of Thibiuca was suppressed |
| 500 | Tunisia | Diocese of Ululi was suppressed |
| 500 | Tunisia | Diocese of Urusi was suppressed |
| 500 | Tunisia | Diocese of Vaga was suppressed |
| 500 | Tunisia | Diocese of Vita was suppressed |
| 500 | Turkiye | Metropolitan Archdiocese of Amida was suppressed |
