Joseph von Laßberg also presents the theory that the tower was built on the site of an earlier destroyed castle. He states that the castle was destroyed by Duke Gotfrid of Alemannia who was at war with Dagobert's successor and rebuilt 80 years later by Charles Martel. From 730 until 911 the Meersburg was a Carolingian castle and owned by the Counts of Linzgau, but administered by the Counts of Buchhorn. Following the extinction of the Buchhorn line, it would have passed to the Counts of Welf. A contract between the Counts of Welf and the Bishopric of Constance indicated that the Meersburg would be given to the Bishopric if the count died without any male heirs. It appears that the Welfs and the Bishopric had close ties, as Bishop Conrad was of Welf descent.
