The ends of the earth
The furthest reaches of the land.
The phrase 'the ends of the earth' derives from the Bible, Zechariah 9:10 (King James Version):
And I will cut off the chariot from Ephraim, and the horse from Jerusalem, and the battle bow shall be cut off: and he shall speak peace unto the heathen: and his dominion shall be from sea even to sea, and from the river even to the ends of the earth.
Caxton used the expression in his 1483 translation of J. de Voragine's Golden Legende:
And all the endes of the erthe shal worshipe the Nacions shal come to the fro ferre and bryngyng yeftes shal worshype in the our lord.
In that passage, and in other religious usages, the phrase was used to indicate the furthest reach of man's dominion, as opposed to the heavens. It wasn't widely used until the 19th century, when it began to be used as we use it today, that is, to mean 'a very long way away'.