Answer: to prevent earthquakes
Explanation: In November 1, 1755, an earthquake happened, releasing the energy equivalent of 32,000 Hiroshima atomic bombs.. Lisbon suffered the worst of it.
After an earthquake, which had destroyed three-fourths of the city of Lisbon, the sages of that country could think of no means more effectual to preserve the kingdom from utter ruin than to entertain the people with a public ritual, it having been decided by the University of Coimbra that the burning of a few people alive by a slow fire, and with great ceremony, is an infallible secret to prevent earthquakes.