In Revelation 21:16 do the walls of the new Jerusalem rise 12,000 furlongs?
There is a difference between walls and walls. In a literal sense there are intruder protective walls, as well as house walls. And in a symbolic sense there are “walls” of water called tsunamis; “walls” of moving snow called avalanches, etc.
A literal interpretation
An explanation of New Jerusalem's huge height is this that the city's top part is of atmospheric nature, shining to produce light, because the Bible says that the Lord is the city's only source of light. Thus, the sun does not seem to exist anymore. And, with no sun the countryside would also need the light coming out from the walls of the city. In other words, the shining Holy City would act like a sun for much of the rest of the earth.
Rev 22:5 (NIV) There will be no more night. They will not need the light of a lamp or the light of the sun, for the Lord God will give them light. And they will reign for ever and ever.
Ps 84:11 (NASB) "the Lord God is a sun and shield"
A symbolic interpretation
A symbolic possibility, on the other hand, is that New Jerusalem is like a soccer ball; with 12 patches. Each tribe’s gate would then be a pearl seen from a distance (referring to the ball and/or the patches)
[At this stage in the discussion it must be pointed out that most translations notes the measurements of New Jerusalem in furlongs and stadia, which is 12000 furlongs/stadia. Not 1500 miles, as NASB has it, or 2400 km, as CEV has it.]
In this symbolic scenario “length, width, and height” stand for the following three different twelfths:
The 1st twelfth, the length, stands for the number of tribes. "Furlong/stadia" in the text (Rev 21:16) would then symbolically mean "populations". The 2nd twelfth, the width, would refer to the number of thousands of people in each tribe, and together with the length would equal 144000. The verse about the 144 cubit thick wall in Rev 21:17, would then be a symbolic people count of the twelve "foundations" of the city, and cubit would stand for 1000.
And he measured its wall, one hundred forty-four cubits, the measure of man, that is of the angel. (BLB)
Thus, the symbolic length of New Jerusalem is 12 tribes; the symbolic width is 12 thousand people; together equaling a 144000 thick "wall" of people.
And lastly the 3rd twelfth, the height, would then refer to how many settlements there will be on the New Earth. If so, an intriguing possibility emerges: There will be twelve different New Jerusalems, with possibly eleven under construction at any given time. If so, there certainly will not be any eternal idleness in the New Earth.
Moreover, if a single wall does not surround a single New Jerusalem the text could, besides referring to a "wall" of people, also refer to walls “around town”. Thus, they could refer to house walls, especially the front walls, the ones facing the streets. The front walls of the houses of each New Jerusalem “suburb” then might be clad with gems, or mosaic tiles, from their respective gemstone.
"Jasper” is mentioned first so it is possible that "Jasper" is the capital of the twelve parts of New Jerusalem, and the place of God’s throne. And if the other cities, or suburbs, originally do not exist, they will be constructed later by the 144000 (Mat 7:13,14), who then first will occupy "Jasper City".
Furthermore, the use of the word “wall” in the head count of the population might mean that the 144000 like a moving tsunami wall will travel between the twelve parts of New Jerusalem, changing settlement twelve times a year. Twelve annual migration waves, in other words. The depiction of the tree of life growing on both sides of the river of life, bearing healing leaves and nourishing fruit twelve times a year, could be a symbolic rendition of this event. (Rev 22:2)
So, the answer to the question: "In Revelation 21:16 do the walls of the new Jerusalem rise 12,000 furlongs?"; is that it all comes down to if it was a literal or symbolic vision John saw?