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Massimo Massimi (10 April 1877 – 6 March 1954) was an Italian Cardinal of the Roman Catholic Church who served as Prefect of the Apostolic Signatura in the Roman Curia from 1946 until his death, and was elevated to the cardinalate in 1935.
Massimi was born in Rome to Prospero Massimi, a lawyer, and his wife Luisa Guerra. Baptized in the church of Santa Maria in Portico, he studied at the Pontifical Roman Seminary (from where he obtained his doctorates in theology and canon law) alongside Eugenio Pacelli, the future Pope Pius XII. He then attended the University of Rome, earning a doctorate in civil law. Massimi was ordained by Archbishop Giuseppe Ceppetelli on 14 April 1900, in the Lateran Basilica.
While doing pastoral work in Rome until 1908, he was named a professor at the "Institutions of Civil Law" of the Pontifical Roman Athenaeum S. Apollinare on 18 November 1904. He entered the Roman Curia on 20 October 1908, as a Promoter of Justice in the Roman Rota. Raised to the rank of Privy Chamberlain of His Holiness on 18 May 1911, Massimi was later made auditor (29 November 1915), pro-dean (19 February 1924), and dean (1 May 1926) of the Roman Rota.
On 21 September 1932, Massimi was appointed president of the commission that was to draw up a project of law on the judicial and procedural regulations of the tribunal of Vatican City. Pope Pius XI created him Cardinal-Deacon of Santa Maria in Portico in the consistory of 16 December 1935. Massimi was made President of the Pontifical Commission for the Codification of Oriental Canon Law on 17 February 1936, and served as a cardinal elector in the 1939 papal conclave that selected Pope Pius XII, who named him President of the Pontifical Commission for the Interpretation of the Code of Canon Law on 14 March 1939.
After ten years' standing as a Cardinal Deacon, Massimi opted for the order of Cardinal Priests and his title was elevated pro hac vice in the consistory of 18 February 1946. Pius XII made him Prefect of the Apostolic Signatura, and thus the highest judicial authority in the Church below the Pope himself, on 29 May 1946.
Cardinal Massimi died in Rome, after receiving viaticum a few hours before. Originally buried at the Campo Verano, his remains were later transferred in October 1976 to the church of Santa Maria in Portico, which had been the church of his baptism as well as his titular church.
| Dean of the Roman Rota
| Pontifical Commission for the Interpretation of the Code of Canon Law
| Prefect of the Apostolic Signatura