Placidus de Titis was an Olivetan monk and professor of mathematics, physics and astronomy at the University of Pavia

University of Pavia

The University of Pavia is a university located in Pavia, Lombardy, Italy. It was founded in 1361 and is organized in 9 Faculties.-History:...

 from 1657 until his death.
Placidus popularized the system of astrological houses now known as the "Placidian system", current in modern astrology

Astrology

Astrology consists of a number of belief systems which hold that there is a relationship between astronomical phenomena and events in the human world...

.
He did not invent the method; it is acknowledged by the 12th century Hebrew astrologer Abraham Ibn Ezra

Abraham ibn Ezra

Rabbi Abraham ben Meir Ibn Ezra was born at Tudela, Navarre in 1089, and died c. 1167, apparently in Calahorra....

  as the system employed by Ptolemy

Ptolemy

Claudius Ptolemy , was a Roman citizen of Egypt who wrote in Greek. He was a mathematician, astronomer, geographer, astrologer, and poet of a single epigram in the Greek Anthology. He lived in Egypt under Roman rule, and is believed to have been born in the town of Ptolemais Hermiou in the...

, an attribution that was accepted by Placidus.

Placidus was born into the Titi noble family. His father died early, and he was looked after by his mother Cecilia. He studied at the University of Padua

University of Padua

The University of Padua is a premier Italian university located in the city of Padua, Italy. The University of Padua was founded in 1222 as a school of law and was one of the most prominent universities in early modern Europe. It is among the earliest universities of the world and the second...

 where his uncle Girolamo de Titi was professor of theology.
The Duchy of Milan

Duchy of Milan

The Duchy of Milan , was created on the 1st of may 1395, when Gian Galeazzo Visconti, Lord of Milan, purchased a diploma for 100,000 Florins from King Wenceslaus. It was this diploma that installed, Gian Galeazzo as Duke of Milan and Count of Pavia...

 at the time was owned by Habsburg Spain, administered by Archduke Leopold Wilhelm of Austria

Archduke Leopold Wilhelm of Austria

Archduke Leopold Wilhelm of Austria was an Austrian military commander, Governor of the Spanish Netherlands from 1647 to 1656, and a patron of the arts.-Biography:...

. The Archduke showed strong interest in science, especially occult sciences of alchemy and astrology, and Placidus dedicated his astrological house tables to him.

Works

• De motibus directionum coelestium mobilium (1641)
• Physiomathematica sive coelestis philosophia (1650), Placidus' magnum opus, first published as Quaestionum physiomathematicarum libri tres, under the pseudonym of Didacus Prittus Pelusiensis, second edition by C. Francobacci und A. Scirota (pseudonyms of two of Placidus' students, F. Brunnaccio and F. M. Onorato)
• Nuncius astronomicus (1654)
• Il corriere astronomico. (1656)
• Tabulae primi mobilis cum thesibus et canonibus (1657)
• Commentaria in Ptolemaeum de siderum judiciis (1658)
• De siderum judiciis, 2 vols. (1660, 1665)
• De diebus decretoriis et aegrorum decubitu, 2 vols. (1661, 1665)
• Ephemerides coelestium motuum (1661-1665)
• Tocco di Paragone, onde evidamente appare che l' astrologia nelle parte concesse da S. Chiese é vera scienza naturale, nobile e utile quanta la filosofia (1666), in defense of astrology as a natural science.