In the books
In the Song of Ice and Fire novels Selhorys is a settlement under the rule of Volantis. It is located at the confluence of the Rhoyne and the Selhoru. It pays tribute to passing Dothraki khalasars, which can easily reach the city from the western-most edge of the Dothraki sea, which is located not far to the east of the settlement. By the standards of the Free Cities, Selhorys is a middling-sized town, although by the standards of Westeros it would be a small city.
- Selhorys at A Wiki of Ice and Fire (spoilers from the books)