Round Tower dome takes flight over old Copenhagen

For just under ten minutes on Monday, the iconic copper-green dome of the Round Tower hovered above the street before landing safely on the ground to applause and cheers from the crowd.

The scene marked the beginning of a major restoration of the three-tonne dome from 1929.

The dome has started to leak, and new copper plates are now being installed.

The Round Tower is arguably the first actual department building at the University of Copenhagen

Rasmus Agertoft, head of history and outreach at the Round Tower

It had to be taken down to minimise the fire hazard while the hot metalwork is carried out. The restoration itself will take place at the foot of the Round Tower, allowing passers-by to follow the process in real time. At the same time, work is being done on both the platform where the dome is normally positioned, and inside the tower itself.

The full restoration is expected to cost DKK 6 million and will be financed by the Round Tower’s own funds.

When the Round Tower was originally constructed in the 17th century, the building was more than just an architectural landmark on the city skyline. The tower was built as the University of Copenhagen’s (UCPH) observatory and played a key role in the nascent scientific community in the city.

University’s first department building

Completed in 1642 under King Christian IV, the Round Tower was built as the university’s observatory — and was one of the first buildings in Denmark constructed specifically for scientific purposes.

»The Round Tower is arguably the first actual department building at the University of Copenhagen,« says Rasmus Agertoft, head of history and outreach at the Round Tower.

Whereas the university mostly just consisted of lecture halls at this time, the Round Tower was built with the express purpose of allowing university astronomers to conduct systematic observations of the night sky.

The observatory was part of the so-called Trinitatis complex, which consisted of the student church — now the Trinitatis Church — and the university library. In this way, research, teaching, and religion were brought together in one single complex in the heart of the city.

»You couldn’t separate science from Christianity. Looking out into the cosmos was also a way of honouring creation,« says Rasmus Agertoft.

Legacy of Tycho Brahe

The Round Tower was a continuation of a strong Danish astronomical tradition, shaped in particular by the astronomer Tycho Brahe. His large observatory Uranienborg on the island of Hven on the Øresund had pioneered methods that later influenced other astronomers at the University of Copenhagen.

The first director of the Round Tower observatory was Longomontanus, a former student and trusted collaborator of Tycho Brahe. He brought over the expertise from Hven to Copenhagen, where the new observatory was to be used both for research and for the training of new astronomers.

»The idea was that this should be a place of learning. There was a clear apprenticeship mindset, much like the one that had shaped Tycho Brahe’s institution,« says Rasmus Agertoft.

The Round Tower was among the earliest university observatories in Europe and was widely praised at the time, regarded as a technological and scientific masterpiece.

READ ALSO: The University of Copenhagen: From the Middle Ages to a modern public university

Few major discoveries — but lasting significance

The Round Tower is now associated with astronomical history, but astronomical breakthroughs rarely actually happened here. Smoke from the city’s stoves, vibrations from passing horse-drawn carriages, and a lack of space, all made it difficult to carry out precise observations from the tower.

The Round Tower did however play a significant role in the development of multiple scientific disciplines. From the mid-1700s, for example, some of Denmark’s first long-term and precise meteorological measurements were carried out from the top of the tower.

We’ve been preparing for this for a long time, and there’s a huge responsibility when working on a listed building

Jeanette Bursche, director of the Round Tower

The Round Tower also served as a reference point for surveying and cartography. For a period, the centre of the tower even functioned as the zero point for national land measurements in Denmark.

Ole Rømer, who discovered the speed of light, has a direct connection to the Round Tower. While the actual discovery took place in Paris in 1676, some of the measurements in the data were made from the Round Tower.

»In this way, the Round Tower has a small part to play in one of the most important discoveries in the history of astronomy,« says Rasmus Agertoft.

Break with the university

In 1861, the University of Copenhagen’s observatory moved from the Round Tower to a new Østervold Observatory. That same year, the university library moved to Fiolstræde, and with that, the Round Tower ceased to function as a unified university complex in practice.

Since then, the building has served a variety of functions and gradually transitioned into being an independent cultural institution. The Round Tower reopened as an exhibition and cultural venue in 1987, something that it still is today.

The building’s function has changed over time, but the duty to preserve the heritage-listed building remains the same. According to the Round Tower’s director, Jeanette Bursche, restoring the building comes with serious responsibility.

»You can’t take this lightly. We’ve been preparing for this for a long time, and there’s a huge responsibility when working on a listed building,« she says.

She points to the lessons learned from last year’s fire at the Børsen, Copenhagen’s 17th century stock exchange building. This heightened the awareness around safety during restoration work on historical structures.

Return of the observatory

Once the restoration is complete, the observatory will be brought back into use. The Round Tower expects to have personnel operating the telescope,  and to welcome guests to the observatory by the autumn.

The dome itself, however, is expected to be reinstalled already during the spring.

Even though the Round Tower is no longer part of the University of Copenhagen, Rasmus Agertoft reckons that the building is still a part of an important story about the university’s scientific foundations.

»It’s important to understand the roots of modern science. And that’s exactly the story that the Round Tower can help communicate,« he says.

The Round Tower is currently closed to visitors due to the ongoing work but is expected to reopen on 6 February.

This article was first written in Danish and published on 12 January 2026. It has been translated into English and post-edited by Mike Young.