Revelation 21:16
And the city lieth foursquare, and the length is as large as the breadth: and he measured the city with the reed, twelve thousand furlongs. The length and the breadth and the height of it are equal.
Cross-reference
Ezekiel 48:8-9 defines a square holy portion for the sanctuary—the OT prototype of the measured square city in Revelation.
Ezekiel 48:20 describes a square holy district (25,000 cubits per side)—directly parallels the square shape of the New Jerusalem.
Ezekiel 48:35 gives the city's perimeter and name 'The Lord is There'—prefiguring God's presence in the New Jerusalem.
Ezekiel 41:4 measures the Most Holy Place as a 20-cubit cube — a direct typological foreshadowing of the New Jerusalem's cubic shape.
1 Kings 6:2 gives the temple's rectangular dimensions (60×20×30) — contrasting with the New Jerusalem's perfect cube of 12,000 furlongs.
Ezekiel 48:30 gives the north gate measurement of the restored city — a parallel to the New Jerusalem's gates and measurements.