Given a text passage, you need to generate a suitable title as the output. The output title should be one of the words/phrases used in the passage and must be no longer than five words. 

Paragraph:   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 .   Question: what is the suitable title of the passage ?
Gregorian Tower