A.T. Robertson Commentary Revelation 21:12

"having a wall great and high; having twelve gates, and at the gates twelve angels; and names written thereon, which are [the names] of the twelve tribes of the children of Israel:" — Revelation 21:12 (ASV)

Having a wall great and high (εχουσα τειχος μεγα κα υψηλον). John returns, after the parenthesis in verse 11, to the structure in verse 10, only to use the accusative εχουσαν as before to agree with πολιν, but the nominative εχουσα as again with "twelve gates" (πυλωνας δωδεκα). Πυλων is an old word (from πυλη gate) for a large gate as in Lu 16:20 and six times in Rev. for the gate tower of a city wall (Revelation 21:12,13,15,21,25; 22:14) as in 1 Kings 17:10; Acts 14:13. See Eze 48:31ff. for these twelve gates, one for each tribe (cf. Revelation 7:1–8).

At the gates (επ τοις πυλωσιν). "Upon the gate towers."

Twelve angels (αγγελους δωδεκα). As πυλωρο or φυλακες according to Isa 62:6; 2 Chronicles 8:14.

Names written thereon (ονοματα επιγεγραμμενα). Perfect passive participle of επιγραφω.

Which are the names (α εστιν). Just as in Ezekiel's vision (48:31ff.), so here the names of the twelve tribes of Israel appear, one on each gate.