The plague of 1484 spread quickly in the old, narrow, dark and crowded streets of many Italian towns. When it ended, many architects sought ways of improving the cities to make them healthier and less cramped.
Leonardo conceived ideas for a multilayered city, with houses above roads, which were above water. Leonardo drew wide streets placed at right-angles to each other, dwellings of several stories, and navigable canals to connect the city to the sea.
Some of his buildings, with their arched colonnades, reflect classical architecture.