Ignazio Danti, born Pellegrino Rainaldi Danti, was a mathematician, astronomer, Catholic bishop and Italian cosmographer. Ignazio Danti as a boy learned the rudiments of painting and architecture from his father and his aunt, but mathematics and science were his favorite studies.
He became part of the Dominican order on March 7, 1555, changing his first name from Pellegrino to Ignazio. After finishing his studies in philosophy and theology, he ended up in prayer for a short period, but soon devoted himself zealously to mathematics, astronomy and geography.
Around 1567, he was invited to Florence by Cosimo I de 'Medici, Duke of Tuscany, who called him, using his services, to revive his mathematical and astronomical studies in the recently acquired domain. In particular, he had Cosimo as the grand-ducal cosmographer, and he elaborated the maps that decorate the Hall of Cards of Palazzo Vecchio. At the same time Pope Pius V is said to have commissioned Danti to design the construction of one of the Dominican churches and a convent in Bosco Marengo. During his stay in Florence, Danti taught mathematics.
Danti resided at the convent of Santa Maria Novella and designed the armillary sphere and the gnomon that appears at the end of the blind arches on the facade of the church in 1572. He had an intense activity as inventor of scientific instruments, author of widely used texts on the manufacture and use of the astrolabe and astronomy.
Moreover, Danti was chosen to direct the construction of a canal that was to put Florence in communication with both the Mediterranean and the Adriatic. Cosimo I did not live for so long to complete his project and immediately after his death (1574), Danti became a professor of mathematics at the University of Bologna where, between 1575 and 1576, he built the first sundial for the Basilica of San Petronio. During that period, the Danti spent a certain period in Perugia, at the invitation of the governor, during which he prepared the maps of the Republic of Perugia.
On the death of Cosimo I, he left Florence because he did not like his successor Francesco I. He went to Rome where he worked on the geographical maps of the Vatican Palaces, invited for his mathematical merits by Pope Gregory XIII, who named him pontifical mathematician and made member of the Committee for the reform of the calendar. He also placed him in charge of the painters summoned to the Vatican by the Pope, to continue the work brilliantly begun by Raphael during the pontificate of Pope Leo X, and at the same time to draw up maps of ancient and modern Italy.
When the pontiff commissioned the architect Domenico Fontana to repair the port of Claudius, it was Danti who provided the projects. During the period in which he resided in Rome, he published the translation of a part of Euclide's works with some annotations, and wrote the life of the architect Jacopo Barozzi da Vignola, as well as preparing notes for his study on the prospect that he will make later. In recognition of his work, Pope Gregory XIII, in 1583, consecrated him bishop of Alatri in Lazio. Danti showed himself to be a zealous pastor in his new position.
As bishop of Alatri, Danti convened a diocesan synod, corrected many abuses and showed great concern for the poor. He also promoted the establishment of the Annunziata Monastery, which he himself designed and which was recognized as a national monument. Shortly before his death, Pope Sixtus V summoned him to Rome to oversee the arrangement of the great obelisk in the Vatican square.
In addition to the works already mentioned, Danti was the author of the Treaty of the use and factory of the astrolabe with the junta of the planisphere of the Raja; Mathematical Sciences reduced to tables and also a modified and annotated edition of La Sfera by Messer G. Sacrobosco translated by Pier Vincenzio Danti.
He died in Alatri. After his death, to occupy his maths chair at the University of Bologna in 1588 he was called Giovanni Antonio Magini, preferred to Galileo Galilei.