Complex sentence: In the past, it has served as barter trade in exchange for other essential services; it is stated that Alexander the Great carried several sacks full of walnuts which he had to use to pay boatmen to ferry his troops.
Split into simpler sentences: In the past, the walnut has served as barter trade in exchange for other essential services. It is stated that Alexander the Great carried several sacks full of walnuts which he had to use to pay boatmen to ferry his troops.