He was also responsible for the construction of the late Romanesque Cathedral (Dom), built in typical north German 'red-brick' style.

Since 1180 part of Ratzeburg diocesan area formed a Prince Bishopric, whose ruler was sovereign and as such had a vote at the Imperial Diet.

After the 1550 death of its ruler Prince-Bishop Georg von Blumenthal, who feuded with Thomas Aderpul, the bishopric converted to Lutheranism in 1554.

The town was almost completely destroyed in 1693, when Christian V of Denmark reduced Ratzeburg to rubble by bombardment in his unsuccessful attempt to push through his succession to the dukedom against the prevailing House of Hanover.

Ratzeburg briefly was part of the First French Empire during the Napoleonic Wars, afterwards the Duchy of (Saxe-)Lauenburg was awarded in personal union to the Danish crown in the Congress of Vienna.

The grave of Ernst Barlach, perhaps the most notable creative artist to have made his home in Ratzeburg, is located in one of the town's cemeteries.