Gregorian Tower

The Gregorian Tower (Italian: Torre Gregoriana) or Tower of the Winds (Italian: Torre dei Venti) is a round tower located above the Gallery of Maps, which connects the Villa Belvedere with the Apostolic Palace in Vatican City. The tower was built between 1578 and 1580 to a design by the Bolognese architect Ottaviano Mascherino (who was credited with building the Apostolic Palace) mainly to promote the study of astronomy for the Gregorian Calendar Reform which was commissioned by Pope Gregory XIII and promulgated in 1582. It was then also known as the Tower of Winds. The tower is now called the "Specola Astronomica Vaticana", the Vatican Observatory. Four stages of progressive development have occurred since it was first established. The tower was an edifice of great value for astronomical observations made using a sundial as they provided essential confirmation of the need to reform the Julian calendar.

The first stage of building of the tower, as recorded by Leo XIII in his motu proprio Ut mysticam of 1891, is credited to Pope Gregory XIII, Pope from 1572 to 1585. The directive was to build a tower at a suitable location in the Vatican and equip it with the "greatest and best instruments of the time". The design was effected after a series of meetings of the experts who had been appointed to reform the Julian calendar, in use since 45 BC, to verify their proposed reforms. Fr. Christoph Clavius, a Jesuit mathematician from the Roman College, was the expert on the committee who suggested the new system for the observations. The 73 metres (240 ft) tower was then built above the museum and library, flanked by the Belvedere and della Pigna courtyards. The instrumentation for the observation of the sun rays falling over it consisted of a meridian line designed by Ignazio Danti of Perugia. It was in the form of a circular marble plate in the centre, embellished with scientific designs. The tower still remains today, but has undergone improvements over the centuries.

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