 = Gregorian Tower = 
 
 The Gregorian Tower ( Italian : Torre <unk> ) or Tower of the Winds ( Italian : Torre <unk> <unk> ) is a round tower located above the Gallery of Maps , which connects the Villa <unk> with the Apostolic Palace in Vatican City . The tower was built between <unk> and 1580 to a design by the <unk> architect <unk> <unk> ( 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 <unk> . It was then also known as the Tower of Winds . The tower is now called the " <unk> <unk> <unk> " , 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 . 
 
 = = Early history = = 
 
 The first stage of building of the tower , as recorded by Leo XIII in his <unk> <unk> <unk> <unk> of 1891 , is credited to Pope Gregory XIII , Pope from <unk> to <unk> . 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 . <unk> . Christoph <unk> , 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 <unk> and della <unk> courtyards . The instrumentation for the observation of the sun rays falling over it consisted of a meridian line designed by <unk> <unk> 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 . 
 
 = = Second stage = = 
 
 The second stage of construction in the 17th and 18th centuries , when the tower was under the charge of the Vatican <unk> , involved <unk> . Filippo Luigi Gilii , a clergyman of St. Peter 's Basilica . Earlier in 1797 , Pius VI gave approval to placing a Latin inscription <unk> <unk> at the entrance to the upper part of the tower , which was implemented by Cardinal <unk> with plans to enhance the instrumentation system in the tower 's observatory . The original observatory was then set up above the second level of the tower with the agreement of Pope Pius VI . Its instrumentation , apart from many normal devices ( such as meteorological and magnetic equipment , with a <unk> and a small transit and <unk> clock , ) was noted for the <unk> Telescope . The instrumentation facilitated recording of occurrences of eclipse , appearance of comets , <unk> of Jupiter and Mercury ’ s transit . As an addition , under the patronage of Pope Pius X , four <unk> observatory <unk> were also added at strategic locations on the 1 @,@ 300 feet ( 400 m ) long fortification walls , more than a thousand years old . <unk> . Gilii , highly respected as a <unk> with a knowledge of physics , biology , <unk> and the Hebrew language , was in charge of the observatory from 1800 to 1821 . He carried out continuous meteorological observations ( twice a day at 6 AM and 2 <unk> ) conforming to the programme of the <unk> Meteorological Society . While the observation records for seven years were published , the balance data in a manuscript form was preserved in the Vatican Library . Subsequent to Gilii 's death in 1821 , the observatory on the tower was discontinued and the instruments were moved to the observatory at the Roman College . Established in 1787 , it was considered more suitable for making observations than the Vatican . 
 
 = = Third stage = = 
 
 The revival of the observatory on the Gregorian Tower was initiated by the <unk> Francesco <unk> with the approval of Pope Leo XIII . High quality instruments were procured , partly with generous donations from <unk> of London , and the automatic recording instruments were procured from Richard in Paris . A four @-@ inch equatorial , a three @-@ inch transit instrument , and four <unk> clocks with two <unk> , were also procured from the observatory at <unk> . In 1888 , the gift of a 16 inch long telescope to Pope Leo XIII , became a part of the observatory . Father <unk> joined the observatory in 1889 after it was upgraded with more modern instruments . The same year , a second tower was built some 400 metres ( 1 @,@ 300 ft ) away from the main Gregorian Tower , overlooking the Vatican Gardens behind St. Peter 's Basilica on the south @-@ west border . It was built to a diameter of 17 metres ( 56 ft ) with a lower wall thickness of 4 @.@ 5 metres ( 15 ft ) , which could bear the load of a 13 inch photographic <unk> , newly procured from Paris . <unk> Father Rodriguez was the expert meteorologist who held the post of director from 1898 to 1905 . In 1891 , Pope Leo XIII , <unk> the <unk> <unk> <unk> <unk> , designated the second tower as the seat of the newly established Vatican Observatory , a decision which required altering the roof to provide a flat terrace for astronomical observations . 
 
 = = Fourth stage = = 
 
 The fourth stage involved <unk> the problem of communicating between the two towers during the time of Pope Pius X. His plans were to make the Gregorian Tower into a historical tower and to record and carry out observations at the second tower by linking the two towers along the fortified wall with a 83 metres ( 272 ft ) iron bridge spanning the gap . At the west end of this bridge , a four @-@ inch equatorial was installed on semicircular <unk> . The east end of the bridge , above the barracks of the gendarmes , had a <unk> , with a camera attached , used to photograph the Sun ( <unk> ) . A new 16 @-@ inch visual telescope , called Torre <unk> X , was erected in the second tower . As a result of these modifications , the original library was moved to the <unk> Academy <unk> , and the old meteorological and seismic instruments were shifted to the <unk> di <unk> observatory . The new Astronomical Library was housed in two rooms of the building . The two new <unk> machines were used for recording on the <unk> plates . The recorded observations were published along with <unk> notes together with the last two series of the <unk> of stars . Charts were printed on silver bromide paper . 
 
 = = Features = = 
 
 The tower had two floors and a <unk> . On the first floor was the famous <unk> Room or Meridian Room , which was initially an open <unk> . Pope Urban VIII had it enclosed and it was subsequently decorated with long sequences of frescoes painted between 1580 and <unk> by Simon <unk> and the two Flemish artists Paul and <unk> <unk> . Today the tower has paintings by <unk> <unk> and <unk> da <unk> . 
 The <unk> Room , also called the Meridian Hall , was once the residence of Queen Christina of Sweden , then newly converted to Catholicism . The room was further modified by two additions which gave it its current name : a sundial , and a delicate but sophisticated <unk> which was fixed to the ceiling of the Meridian Hall . These were created by <unk> <unk> , the papal <unk> , in association with the Gregorian Calendar Reform . The sundial consisted of a straight line in white marble running across the floor in a north @-@ south direction , intended to measure the height of the Sun at noon according to the seasons of the year . The observations made with the sundial provided essential confirmation of the need to reform the Julian calendar . The <unk> , in contrast , was a complex mechanism attached to the ceiling which was used to measure the strength and direction of the wind but soon stopped functioning . The instrument may have led to the other name of the tower , Tower of the Winds ; however , an ancient observatory at Athens was also called the Tower of the Winds and might have been the source for inspiration . 
 The interior walls and ceiling of the hall were richly decorated , in some cases with <unk> frescoes of the hills and Roman countryside , the <unk> , religious themes , the buildings surrounding the area , and naval <unk> with Jesus calming the storm and so forth . 
 
 