Plato, Laws 778d

ὡς ὁσίων πέρι, τὰ δὲ καὶ τοιούτων θεῶν ἱδρύματα, καὶ ἐν τούτοις δικαστήρια, ἐν οἷς αἵ τε τῶν φόνων πρέπουσαι δίκαι γίγνοιντʼ ἂν καὶ ὅσα θανάτων ἄξια ἀδικήματα. περὶ δὲ τειχῶν, ὦ Μέγιλλε, ἔγωγʼ ἂν τῇ Σπάρτῃ συμφεροίμην τὸ καθεύδειν ἐᾶν ἐν τῇ γῇ κατακείμενα τὰ τείχη καὶ μὴ ἐπανιστάναι, τῶνδε εἵνεκα. καλῶς μὲν καὶ ὁ ποιητικὸς ὑπὲρ αὐτῶν λόγος ὑμνεῖται, τὸ χαλκᾶ καὶ σιδηρᾶ δεῖν εἶναι τὰ τείχη

partly because therein they deal with holy matters, and partly because they are the seats of holy gods; and in these will fittingly be held trials for murder and for all crimes worthy of death. As to walls, Megillus, I would agree with your Sparta in letting the walls lie sleeping in the ground, and not wake them up, and that for the following reasons. It is a fine saying of the poet, and often repeated, that walls should be made of bronze and iron