Hammershus, the Round Churches of Bornholm & the Baltic Crusades

Hammershus, the Round Churches of Bornholm & the Baltic Crusades

A Guided Tour: Hammershus, the Round Churches of Bornholm and the Baltic Crusades

Your journey begins at the north tip of Bornholm, where the dramatic granite cliffs of Hammerknuden plunge into the Baltic. Rising from this headland are the ruins of Hammershus, the largest castle ruin in northern Europe and one of Scandinavia's most commanding medieval fortifications.

Construction began around 1160, initiated by Denmark’s king Valdemar I, who needed a stronghold for his crusades in order to muster troops and gather supplies. From the castle ruins, you can look out over the Baltic: on a clear day you can see the Swedish coast. Hammershus was built to see and be seen - a statement of power in a sea contested by the Hanseatic League, Wendish tribes to the south and the crusading orders further east.

As you explore the castle ruins - from the 14^th century bridge to the inner tower keep, foundations of great hall and church and cannon emplacements overlooking the Baltic Sea, your guide explains the 800-year-old history of Hammershus – from impregnable medieval fortress to national historic monument. In 1658, when Bornholm was occupied by Swedish troops during the Dano-Swedish War, the people of Bornholm rose in revolt and killed the Swedish commandant, handing the island back to the Danish king. The island has remained part of Denmark ever since. It was decommissioned as a fortress in 1743 and systematically quarried for building stone. It became Denmark’s first national historic monument in 1822.

Round Churches: Fortresses of the Faith

From Hammershus, you travel southeast across Bornholm’s granite countryside to encounter something unique in all of Scandinavia: four medieval round churches, built in the 12^th and 13^th century and unlike anything else in Denmark.

Round Church of Østerlars

The largest and most dramatic of the four round churches, Østerlars dates to around 1200. Its massive whitewashed cylindrical tower - three storeys high - was built simultaneously as a place of worship, a mustering point and storage facility. Inside, your guide draws your attention to the frescoes that still glow faintly on the plaster - depicting the Last Judgment and scenes from the Bible for an illiterate medieval congregation.

Round churches of Nylars, Olsker & Nyker

The other three round churches each have their own character. Nylars retains some of the finest Romanesque frescoes on the island, depicting the Creation. Olsker is the tallest and most slender - almost tower-like. Nyker is the smallest and most intimate.

Why round?

Here your guide pauses for the central historical question. Why did Bornholm's medieval builders choose this unusual form? Several theories converge:

Crusading inspiration: the round form echoes the Church of the Holy Sepulchre in Jerusalem - a shape adopted across Europe for exactly this symbolic reason.

Practical strength: the circular design is structurally superior for withstanding attack.

The Baltic Crusades: The Wider World These Stones Remember

This brings your guide to the broader historical canvas. The round churches and Hammershus were not built in isolation - they were products of a violent, expansionary age known as the Northern Crusades (roughly 1147-1410).

While crusaders marched to Jerusalem, a parallel holy war was being waged on the Baltic's eastern and southern shores. Danish kings, Swedish lords, German bishops, and crusading military orders - above all the Teutonic Knights and the Livonian Brothers of the Sword - pushed into pagan Prussia, Livonia (modern Latvia and Estonia), Lithuania, and Finland, converting or conquering as they went.

Bornholm’s role was both strategic and symbolic. As a mid-Baltic island, it sat on the trade and military routes connecting Novgorod, the Hanseatic League states and the crusading heartlands of modern-day northern Germany and Poland with the conquest frontiers in Livonia and Estonia. Danish kings used the island as a staging point and supply base.

Bringing It Together: A Medieval Island at the Centre of a Crusading World

As your tour ends, perhaps watching the sunset over the Baltic from Hammershus, your guide offers a final reflection. Bornholm is often seen today as a peaceful summer idyll - herrings and smokeries and bicycle paths. But its stones tell a different story. The round church builders, Hammershus, the trade routes threading past this granite rock - all connect this small island to one of the most dramatic episodes of medieval European history: the Christianisation of the Baltic world by sword, cross, and castle.

Practical notes for visitors: Hammershus is freely accessible year-round, but requires good physical motility and suitable walking shoes. Østerlars and the other round churches are open to visitors from spring through autumn, with small admission fees.