Uranienborg (Uraniborg) was a Danish astronomical observatory operated by Tycho Brahe. It was built circa 1576-1580. Shortly after its construction the observatory was expanded with an underground facility, Stjerneborg, on an adjacent site. The building was dedicated to Urania, the Muse of Astronomy and named Uranienborg, "The Castle of Urania." It was the first custom-built observatory, and the last to be built without a telescope as its primary instrument.
The main building of Uraniborg was square, about 15 meters on a side, and built mostly of red brick. Two semi-circular towers, one each on the north and south sides of the main building, giving the building a somewhat rectangular shape overall. The observatory had a large mural quadrant affixed to a north-south wall, used to measure the altitude of stars as they passed the meridian. This, along with many other instruments of the observatory, was depicted and described in detail in Brahe's 1598 book Astronomiae instauratae mechanica.
A large wall, 75 meters on a side and 5.5 meters high was planned to surround Uraniborg, but never built, instead a high earth mound was constructed and lasted until today being the only remnant of the observatory still in place. Uraniborg was located in the very middle, with an extensive set of intricate gardens between the mound walls and the building. In addition to being decorative, the gardens also supplied herbs for the Tycho's medicinal chemistry experiments. The gardens are currently being re-created, using seeds found on-site or identified in Tycho's writings.
Uraniborg was an extremely expensive project. It is estimated that it cost about 1% of the entire state budget during construction.
Shortly after construction it became clear that the tower-mounted instruments were too easily moved by wind, and Tycho set about constructing a more suitable observation site. The result was near Stjerneborg a smaller site built entirely at ground level and dedicated purely to observations. The basic layout was similar to Uraniborg, with a wall of similar shape surrounding the site, although the enclosed area was much smaller. The instruments were all placed underground, covered by opening shutters or a rotating dome in buildings built over the instrument pits.
Upon losing financial support from the new king, Christian IV of Denmark, Tycho abandoned Hven in 1597 and both Uraniborg and Stjerneborg were destroyed shortly after Tycho's death. Stjerneborg was the subject of archaeological excavations during the 1950s, resulting in the restoration of the observatory. Stjerneborg now houses a multimedia show. The Round Tower in Copenhagen was inaugurated in 1642 as a replacement. The grounds are currently being restored.References:
The city walls of Avila were built in the 11th century to protect the citizens from the Moors. They have been well maintained throughout the centuries and are now a major tourist attraction as well as a UNESCO World Heritage Site. Visitors can walk around about half of the length of the walls.
The layout of the city is an even quadrilateral with a perimeter of 2,516 m. Its walls, which consist in part of stones already used in earlier constructions, have an average thickness of 3 m. Access to the city is afforded by nine gates of different periods; twin 20 m high towers, linked by a semi-circular arch, flank the oldest ones, Puerta de San Vicente and Puerta del Alcázar.