Before refrigeration, the use of natural ice as a food preservative presented logistical problems of time, transportation, and cold storage. Glaciers may have been the forerunners of ice chests and icehouses. One supposition about Ice Age food harvesting suggests that early humans hacked through glacial ice into the carcasses of mastodons that may have been frozen for millennia. Later technology involved the shaping and placement of ice onto food. Zimri-Lin, an Iraqi monarch, constructed an icehouse near the Euphrates River in 1700 BCE. As early as 1000 BCE the Chinese cut ice for kitchen use and for preserving melons and fruit in ground caches. At Yongcheng in Shensi Province, a palace ice pit survives from around 600 BCE. Insulated with rice husks, cached foodstuffs were accessible through sluice gates. Melted ice drained away through a channel to the river.