Albert Barnes on Revelation 21:14

And the wall of the city had twelve foundations. It is not said whether these foundations were twelve rows of stones placed one above another under the city, and extending round it, or whether they were twelve stones placed at intervals. The former would seem to be the most probable, as the latter would indicate comparative feebleness and liability to fall. Compare Barnes on "Re 21:19.

And in them. In the foundation of stones. That is, the names of the apostles were cut or carved in them so as to be conspicuous.

The names of the twelve apostles of the Lamb. Of the Lamb of God; the Messiah. For an illustration of this passage, Eph 2:20.

(o) "and in them" Eph 2:20