Darkness in a dream usually points to the unknown -- the unconscious part of a situation, or of yourself, that hasn't been illuminated yet. Moving through it without panic can reflect a growing willingness to face uncertainty, while fear of the dark often names a more specific worry about what you might discover if you looked closer.
Every city built with Mars in the Midheaven, or any other fixed star from the same nature, will see the majority of its governors die by the sword. - Ptolomeus