Trøjborg Slotsruin is located approximately 12 km north of Tønder in Visby in Sønderjylland. The name Trøjborg probably originates from the Greek Troja.
The castle was built in the 1300s on a 30 × 30 m large bench. Trøjborg is mentioned in 1347 in a letter from Duke Valdemar of Sønderjylland as Duke Valdemar Atterdags castle. In 1407 it came to Queen Margretes possession, but later it was pledged to Ribe bishop chair.
After the Reformation in Denmark in 1536, the carnivore praised the crown, and King Frederik 2. surrendered the fortune to Daniel Rantzau as a thank-you for his merits in the war against the Swedes. Around 1580, Peter Rantzau drove the original medieval castle instead of constructing a renaissance castle on the spot. When the Rantzau family died in 1658, the castle slowly declined.
In the first half of the 19th century Johan Ferdinand was the owner of Neergaard. In 1851 Trøjborg was bought by farmer Knud Lausten Knudsen, who planned to set up a teacher’s seminar on the spot, but when these plans were not realized, the castle was demolished in 1854. However, parts of the south wall and the basement were preserved.