The upper stage is built on one Shuttle main engine.
In the 15th century the upper stage was added which now houses the bells.
It is known that the upper stage was added in the 17th century.
This required a larger upper stage, and was heavier as well.
It was used as the upper stage, and provided improved performance.
There is also a clock on each side, at the top of the upper stage.
The upper stage of the tower was rebuilt in the 17th century.
Due to a problem with its upper stage it failed to leave low Earth orbit.
The lower part of the tower was built around 1300 with the upper stages being added in the 15th century.
It was supposed to be interactive with other players, in its upper stages.