In describing the Duke's love of the bizarre, the narrator notes that although most palaces have rooms that "form a long and straight vista," the Duke's rooms
. . . were so irregularly disposed that the vision embraced but little more than one at a time. There was a sharp turn at every twenty or thirty yards, and at each turn a novel effect. . . . Now in no one of the seven apartments was there any lamp or candelabrum. . . . There was no light of any kind. . . .
The Duke has arranged his rooms so that no one can see the actual extent of the space available. The fact that sharp turns occur "with novel effect" implies that the Duke wants to create space that is secretive, that cannot be navigated in a linear fashion, and, most important, will confuse anyone who is not familiar with the lay out of the palace. In other words, the palace is designed to confuse and to prevent unwanted guests from penetrating its interior. The only lighting is indirect, provided by charcoal braziers that reflect light through stained-glass windows, creating not light but a series of grotesque shadows in the various rooms. In the most westward of the rooms, the seventh, the light is so diffuse, and the decorations within the room so black, that very few revelers wish to enter.
All the rooms have a different color scheme--blue, purple, green, orange, white, and violet--but the seventh is black, with scarlet window panes:
[the effect] was ghastly in the extreme, and produced so wild a look upon the countenances of those who entered, that there were few of the company bold enough to set foot within its precincts at all.
To completely unnerve his guests, the Duke has placed a "clock of ebony" in the seventh room whose hourly signal is so disturbing that the "musicians were constrained to pause," and the all the revelers stop to listen to the clock's chimes. The seventh room, whose color scheme is black, the symbol of mortality, scares everyone because it not only represents death but also contains a clock whose hourly chime reminds its listeners that time is running out. Prince Prospero, in creating a room that symbolizes death, has made a serious tactical error in his attempt to cheat death--he has, in effect, challenged the Red Death to a duel.
When the spectral figure appears--"shrouded in head to foot in habiliments of the grave"--and makes his way slowly through all the rooms, ending his deliberate walk in the black room where Prince Prospero attempts to attack him and drops dead for his efforts, the revelers realize that they are in the presence of the Red Death, the one thing they have desperately tried to avoid, and they, like the Duke, begin to drop.
Prince Prospero's bizarre and unusual lay-out of the rooms is designed very skillfully to keep the Red Death from successfully penetrating the palace. The twists and turns, the indirect lighting--all this should have prevented an adversary from penetrating to the heart of the palace, the black room. Unfortunately, Prince Prospero and his revelers failed utterly to anticipate their real enemy--death itself--and they paid the price all mortals must pay for having lived.