Standing at tall and affectionately referred to by the city's inhabitants as "Steffl" (a diminutive form of "Stephen"), St. Stephen's Cathedral's massive south tower is its highest point and a dominant feature of the Vienna skyline. Its construction lasted 65 years, from 1368 to 1433. During the Siege of Vienna in 1529 and again during the Battle of Vienna in 1683, it served as the main observation and command post for the defence of the walled city, and it even contains an apartment for the watchmen who, until 1955, manned the tower at night and rang the bells if a fire was spotted in the city. At the tip of the tower stands the double-eagle imperial emblem with the Habsburg-Lorraine coat of arms on its chest, surmounted by a double-armed apostolic cross, which refers to "Apostolic Majesty", the imperial style of kings of Hungary. This emblem replaced earlier crescent and the six-pointed star emblem. The original emblem, as well as a couple of later ones, today can be seen at the Vienna City Museum.