Laodicea on the Lycus (Greek: Λαοδίκεια πρὸς τοῦ Λύκου; Latin: Laodicea ad Lycum, also transliterated as Laodiceia or Laodikeia, earlier known as Diospolis and Rhoas; modern Turkish: Laodikeia) was the ancient metropolis of Phrygia Pacatiana (also attributed to Caria and Lydia), built on the river Lycus (Çürüksu), in Anatolia near the modern village of Eskihisar (Eski Hissar), Denizli Province, Turkey.

The ruins near Denizli (Denisli) are well preserved and as of 2012 are being substantially renovated. Its many buildings include a stadium, baths, temples, a gymnasium, theatres, and a bouleuterion. On the eastern side, the line of the ancient wall may be distinctly traced, with the remains of the Ephesus gate; there are streets traversing the town, flanked by colonnades and numerous pedestals. North of the town, towards the Lycus, are many sarcophagi, with their covers lying near them, partly imbedded in the ground, and all having been long since rifled.

West Baths Particularly interesting are the remains of an aqueduct starting several kilometres away at the Baspinar spring in Denizli, and possibly having another more distant source. Unusually, to cross the valley to the south of Laodicea, instead of the usual open channel carried above the level of the city on lofty arches as was the usual practice of the Romans, an inverted siphon was employed consisting of a double pressurised pipeline, descending into the valley and back up to the city. The low arches supporting the siphon commence near the summit of a low hill to the south where the header tank was located, and thence continue to the first terminal distribution tank (castellum aquae) at the edge of the hill of the city, whose remains are visible to the east of the stadium and South Baths complex. The water was heavily charged with calcareous matter, as several of the arches are covered with a thick incrustation where leaks occurred at later times. The siphon consisted of large carved stone pipes; some of these also are much incrusted, and some completely choked up. The terminal tank has many clay pipes of various diameters for water distribution on the north, east and south sides which, because of the choking by sinter, were replaced in time. To the west of the terminal is a small fountain next to the vaulted gate. The aqueduct appears to have been destroyed by an earthquake, as the remaining arches lean bodily on one side, without being much broken. A second distribution terminal and sedimentation tank is visible 400 meters (1,300 ft) north of the first, to which it was connected via another siphon of travertine blocks, and this one is bigger and supplied most of the city.
The stadium, which is in a good state of preservation, is near the southern extremity of the city. The seats are arranged along two sides of a narrow valley, which appears to have been taken advantage of for this purpose, and to have been closed up at both ends. Towards the west are considerable remains of a subterranean passage, by which chariots and horses were admitted into the arena, with a long inscription over the entrance. The city ruins bear the stamp of Roman extravagance and luxury, rather than of the stern and massive solidity of the Greeks. Strabo attributes the celebrity of the place to the fertility of the soil and the wealth of some of its inhabitants: among whom Hiero, having adorned the city with many beautiful buildings, bequeathed to it more than 2000 talents at his death.