Adam Clarke on Revelation 21:16

The city lieth foursquare - Each side was equal, consequently the length and breadth were equal; and its height is here said to be equal to its length. It is hard to say how this should be understood. It cannot mean the height of the buildings, nor of the walls, for neither houses nor walls could be twelve thousand furlongs in height; some think this means the distance from the plain country to the place where the city stood. But what need is there of attempting to determine such measures in such a visionary representation? The quadrangular form intimates its perfection and stability, for the square figure was a figure of perfection among the Greeks; αντρ τετραγωνος, the square or cubical man, was, with them, a man of unsullied integrity, perfect in all things.