Rashi on Numbers 31:10/רש"י על במדבר ל״א:י׳

1טירתם means the place of their scribes (notarii) — a term which is denoting the dwelling-place of their priests, those well acquainted with their laws (cf. Siphre). Another explanation is that it means the place of their princes, just as “the lords of the Philistines” (I Samuel 6:4) is translated in the Targum by “the טורני of the Philistines” (Sifrei Bamidbar 157:5).