According to Saxo Queen Thyra began the construction of the Danevirke earthworks to defend against attacks from the south. Today archaeology has established that the first Danevirke was constructed as early as the 700s, or perhaps even before this. This knowledge was not available in the 19th century and Queen Thyra became one of the great national symbols during the Danish-German wars of the period.

Thyra in the role as initiator behind the Danevirke is reproduced numerous times. The most well-known example is an etching by Lorenz Frølich (1820-1908). This national romantic picture shows an active, energetic queen. It was originally a sketch for the decoration of a new government building in Flensborg, but was rejected. The sketch was published by the art association in Flensborg, and since has been published and used in numerous contexts. Behind the motif lies the hope that the Dannevirke will stand firm against the German threat. The atmosphere of the time just after the defeat in 1864 finds expression in the painting by Christen Dalsgaard (1825-1907) of Queen Thyra sitting in front of a massive Danevirke.