ope ▁Honor ius ▁IV ), ▁ 1 2 8 7 — 1 2 8 8 ▁( P ope ▁Nicholas ▁IV ), ▁and ▁ 1 2 9 2 — 1 2 9 4 ▁( P ope ▁Cel est ine ▁V ) — oc cur red ▁sans ▁conc lave , ▁often ▁at ▁great ▁length . ▁Cel est ine ▁V , ▁whose ▁election ▁took ▁two ▁years ▁and ▁three ▁months , ▁re inst ated ▁the ▁conc lave ▁with ▁a ▁series ▁of ▁three ▁decre es , ▁and ▁his ▁successor , ▁Pope ▁Bon if ace ▁VIII ▁restored ▁the ▁conc lave ▁by ▁his ▁" Reg ula e ▁I ur is ". ▁ ▁References ▁ ▁Bibli ography ▁ ▁Francesco ▁Crist of ori , ▁Il ▁conc lave ▁del ▁M CC L XX ▁in ▁V iter bo ▁( R oma - S ien a - V iter bo ▁ 1 8 8 8 ). ▁▁ ▁Antonio ▁Fran chi , ▁Il ▁conc lave ▁di ▁V iter bo ▁( 1 2 6 8 - 1 2 7 1 ) ▁e ▁le ▁sue ▁orig ini : ▁s aggio ▁con ▁document i ▁in ed iti ▁( Ass isi : ▁Por zi un cola , ▁ 1 9 9 3 ). ▁ ▁Andreas ▁Fischer , ▁K ardin ä le ▁im ▁Kon k lave : ▁die ▁lange ▁Sed is v ak ant z ▁der ▁Jahre ▁ 1 2 6 8 ▁bis ▁ 1 2 7 1 ▁( Ber lin : ▁Walter ▁de ▁Gru yter ▁ 2 0 0 8 ), ▁ ▁Category : 1 3 th - century ▁elections