Acts 12:10

When they were past the first and the second ward
Or watch, which were set within the prison, and might be some of the quaternions of soldiers to whom Peter was delivered; two of them were with him, and others might be placed at these two wards for further security; and these circumstances make the deliverance the more wonderful and remarkable; the watch must either be asleep, or their eyes were holden, or the angel and Peter passed by so swiftly that they were unobserved:

they came unto the iron gate that leadeth unto the city:
which was not one of the gates of the city, as if the prison was without the walls of it; but was the great and strong gate of the prison, which for the security of the prisoners was made of iron, and this gate led directly into the city of Jerusalem:

which opened to them of his own accord;
as the gates of the temple are said to do ^F7, forty years before the destruction of Jerusalem: this was done by a divine power; and because no human creature had any hand in it, it is said to be done of its own accord:

and they went out.
The Cambridge copy of Beza's adds, "they went down seven steps"; that is, from the prison into the city:

and passed on through one street;
what street this was is not certain; there were several streets in Jerusalem: (See Gill on Acts 9:11) and forthwith the angel departed from him: he being now safe and out of danger, he left him to himself, to betake himself to what house he should think fit.