Rundetaarn (The Round Tower) was built on the initiative of King Christian IV (1588-1648) with Hans Steenwinkel the Younger as the architect. On 7 July, the foundation stone for Rundetaarn was laid. The tower was the first stage of the Trinitatis complex, which was to gather three important facilities for the scholars of the seventeenth century: an astronomical observatory, a student church and a university library. Aerial view of Round Tower
	Uppermost on the facade of the tower there is a gilded inscription, a rebus. Christian IV's draft of it, written with his own hand, is kept at the Danish Record Office. The rebus can be interpreted in the following way: Lead God, the right teaching and justice into the heart of the crowned King Christian IV, 1642. 1642 was the year when the tower was completed.
	The spiral walk is unique in European architecture. The 209 m long spiral ramp winds itself 7,5 times round the hollow core of the tower, forming the only connection between the individual parts of the building complex.
	From the platform, 34.8 m above the street, the visitor has a magnificent view of the old part of Copenhagen. Along the edge of the platform runs a beautiful wrought-iron lattice made in 1643 by Kaspar Fincke, Court Artist in metalwork. In the latticework, Christian IV's monogram and the letters RFP are seen; these letters represent the King's motto: Regna Firmat Pietas - Piety strengthens the Realms.
	Rundetaarn is the oldest functioning observatory in Europe. Untill 1861 it was used by the University of Copenhagen, but today, anyone can observe the night sky through the fine astronomical telescope of the tower in the winter period.
	The library hall, above the vaults of the Church of Trinitatis, was used as a university library in the years 1657 - 1861. In 1987, the hall was reopened after thorough restoration, and the 900 m2 of the room now serve as the framework for changing exhibitions of art, culture, history and science. Every year you can listen to around 100 concerts in the library hall.
	King Christian IV's beautiful and characteristic edifice, with its many possibilities, is a live part of the cultural environment of Copenhagen.