When Tokugawa Ieyasu decided to make Edo his new political capital in the early years of the 17th century, he had the city laid out according to mystical beliefs about auspicious locations and lucky or unlucky directions.
Derived from the ancient Chinese philosophy of yin and yang, which holds that these two forces of the universe must be in balance to produce harmony, a Japanized system of astrology, geomancy and offensive or defensive magic had, by then, been important in decision-making for around 1,000 years. Today, many popular beliefs, such as those determining appropriate dates for weddings or funerals, still derive from this ancient practice.
According to these beliefs, the northeast is a direction vulnerable to intrusion by evil spirits, and so in a city it needs to be fortified with religious buildings. But in order to reinforce this protection, the opposite -- southwest -- direction must also be fortified.
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