Midrash for Ketubot 90:16

"in one of your cities": What is the intent of this? Because it is written (Ibid. 5) "Then you shall take out that man or that woman who did this evil thing, to your cities (lit., "gates"), I might think, the reference is to the gate (i.e., the beth-din) in which he was judged; it is, therefore, written "gates" (verse 2), "gates" (verse 5). Just as "gates" (2) refers to the city in which they were found and not to the gate (beth-din) in which they were judged, so, "gates" (5) refers to the city in which they were found and not to the gate (beth-din) in which they were judged.