1 2 3 4 "Works of Man", Ronald W. Clark, ISBN 0-670-80483-5 (1985) 352 pages, Viking Penguin, Inc, NYC, NY, quotation page 87: "There was little experience moving bulk loads by carts, while a packhorse would [sic, meaning 'could' or 'can only'] carry only an eighth of a ton. On a soft road a horse might be able to draw 5/8ths of a ton. But if the load were carried by a barge on a waterway, then up to 30 tons could be drawn by the same horse."
↑ Lạc đà có thể mang tới 600 cân cho quảng đường ngắn
