Ascending Compensating Double Horn Gebr. Alexander, Mainz (D), ca 1930 During the 1930's, most professional Belgian horn players switched to double horns that had become available. Although local workshops as Mahillon and Persy had developped double horns at that time, the preference of most players was to get hold on an Alexander, built in the German town of Mainz. The models with an ascending 3rd valve were popular in Belgium until the late 20th century. At the creation of the Belgian national orchestra, the players were provided with instruments of this type.