What two islands were the farthest north on Egyptian trade routes?

Described by Herodotus as a road "traversed ... in forty days," it became by his time an important land route facilitating trade between Nubia and Egypt. Its maximum extent was northward from Kobbei, 25 miles north of al-Fashir, passing through the desert, through Bir Natrum and Wadi Howar, and ending in Egypt.

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