How did the ancients preserve ice cubes?

Take ice from the river in winter, put it in a cellar or an ice room, cover it with a quilt (or sawdust), and isolate it from air exchange and temperature exchange with the outside world. At first, only the royal family and powerful families had the manpower and material resources to operate the ice house (the ice house is generally large, so the bigger the ice house, the more constant temperature and the more heat preservation; Secondly, the official population is large and the losses are great. What luxury do you like to eat in summer, such as iced watermelon or iced plum juice?