John the Apostle
Revelation 21:16ESV·traditional attribution

The city lies foursquare, its length the same as its width. And he measured the city with his rod, 12,000 stadia. Its length and width and height are equal.

Matthew Henry Presbyterian @wholebiblehenry

We have already considered the introduction to the vision of the new Jerusalem in a more general idea of the heavenly state; we now come to the vision itself, where observe, I. The person that opened the vision to the apostle - one of the seven angels, that had the seven vials full of the seven last plagues, Rev 21:9.

Commenting on Revelation 21:9-27

John Gill Reformed Baptist @doctorgill

And the city lieth four square,.... To the four corners of the world, from whence its inhabitants come, and denotes the regularity, uniformity, perfection, and immovableness of it. And the length is as large as the breadth; this church state will be all of a piece, perfect, entire, and wanting nothing.

Albert Barnes Presbyterian @notesbybarnes

Verse 16. And the city lieth four-square. It was an exact square. That is, there was nothing irregular about it; there were no crooked walls; there was no jutting out, and no indentation in the walls, as if the city had been built at different times without a plan, and had been accommodated to circumstances.