Mencius - Book 2, Part 2, Chapter 1A

Mencius said, 'Opportunities of time vouchsafed by Heaven are not equal to advantages of situation afforded by the Earth, and advantages of situation afforded by the Earth are not equal to the union arising from the accord of Men.

'There is a city, with an inner wall of three lî in circumference, and an outer wall of seven. The enemy surround and attack it, but they are not able to take it. Now, to surround and attack it, there must have been vouchsafed to them by Heaven the opportunity of time, and in such case their not taking it is because opportunities of time vouchsafed by Heaven are not equal to advantages of situation afforded by the Earth.

'There is a city, whose walls are distinguished for their height, and whose moats are distinguished for their depth, where the arms of its defenders, offensive and defensive, are distinguished for their strength and sharpness, and the stores of rice and other grain are very large. Yet it is obliged to be given up and abandoned. This is because advantages of situation afforded by the Earth are not equal to the union arising from the accord of Men.
~ James Legge translation via nothingistic.org ~

Go here to read the introductory post to this serialized version of the Works of Mencius.