When they were past (dielthontes). Second aorist active participle of dierchomai, transitive with dia in composition.
The first and the second ward (prōtēn phulakēn kai deuteran). It is not clear to what this language refers. Some take it to mean single soldiers, using phulakēn in the sense of a guard (one before the door, one at the iron gate). But it seems hardly likely that the two soldiers with whom Peter had been stationed are meant. Probably the “first ward” means the two soldiers of the quaternion stationed by the door and the second ward some other soldiers, not part of the sixteen, further on in the prison by the iron gate. However understood, the difficulties of escape are made plain.
Unto the iron gate that leadeth into the city (epi tēn pulēn tēn sidērān tēn pherousan eis tēn polin). Note the triple use of the article (the gate the iron one the one leading into the city). For this resumptive use of the article see Robertson, Grammar, pp. 762, 764. This iron gate may have opened from a court out into the street and effectually barred escape.
Opened to them (ēnoigē autois). Second aorist passive indicative of anoigō, the usual later form though ēnoichthē (first aorist passive) occurs also, was opened.
Of its own accord (automatē). Old compound adjective (autos, self, obsolete maō, to desire eagerly, feminine form though masculine automatos also used as feminine). In the N.T. only here and Mar 4:28. It was a strange experience for Peter. The Codex Bezae adds here “went down the seven steps” (katebēsan tous hepta bathmous), an interesting detail that adds to the picture.
One street (rhumēn mian). The angel saw Peter through one of the narrow streets and then left him. We have no means of knowing precisely the location of the prison in the city. On “departed” (apestē) see note on Act 12:7.