This paper investigates the methods used in city planning of ancient Chiang Mai, which was founded in CE 1296 by King Mangrai. According to the Chiang Mai Chronicle, King Mangrai invited King Ram Khamhaeng of Sukhothai and King Ngam Muang of Phayao to the new site and consulted them on the suitability of the location and the city plan. Together they observed seven good omens for the site, for example, mountain in the west, river in the east, water reservoir in the northeast, and fertile soil for farming. King Mangrai then decided to establish the Lanna capital city at this site and name Chiang Mai. He spent four years planning, including the determination of the cardinal directions. The city plan chosen was a square formed by moats and city walls that faced the cardinal directions. The starting date and time of construction were chosen according to astrological calculations based on the position of the Sun, the Moon, and the five classical planets. Work began at the Sri Bhumi Corner in the northeast, which was considered the most auspicious of the four corners. The city walls, the observation towers, the gates, the moats, the royal residences, and the Throne Hall were all built at the same time. Most of the work was completed within four months. Unfortunately, written records on the methods used in the city planning do not exist. Nonetheless, the results of this investigation suggest that the Chiang Mai city plan was influenced by the Vaastu Shastra, which is ancient Hindu knowledge about architecture.