In Pamphylia↗ (southern Turkey, in modern terms). Midway between Perge↗ and Aspendos↗; Barrington Atlas map 65 grid E4. (For Side, which lay east of Aspendos↗, see sigma 374.)
The name is more usually found as Sillion, though Stephanus of Byzantium↗ has it as Syleion; cf. under sigma 1338.