Hardegg Castle was first mentioned in 1145. It was probably founded earlier by the Counts of Plain. At that time Hardegg was situated on the northern border of the March of Bohemia and had to protect it against attacks from the north.
During the 14th century, the castle was considerably enlarged under the Counts of Maidburg/Magdeburg.
At its maximum, the castle was equipped with 7 gates and 6 towers. At the end of the 15th century, the counts were so mighty that they fell under Imperial Immediacy.
Until the mid-17th century, Hardegg Castle passed through several noble families until it was acquired by the Khevenhüller-Metsch family, who were Counts and would later become Sovereign Princes. After they moved their residence from Hardegg to nearby Riegersburg Castle in 1730, the castle fell into disuse and dilapidated.
Already in 1764, the local townspeople were allowed to take stones and wood from the abandoned castle to repair their houses after a fire had devastated the town. The castle was turned into a ruin.
In 1878 Prince Johann Carl Khevenhüller-Metsch had part of the castle rebuilt and inserted a family crypt.
At present Hardegg Castle can be visited for a fee. A very nice castle ruin although the castle looked bigger on the outside than it felt on the inside because a fair amount of rooms and areas could not be visited. But still recommended if you are in the area