Tartessos or Tartessus is a harbor city and surrounding culture on the south coast of the Iberian peninsula (in modern Andalusia, Spain), at the mouth of the Guadalquivir River.

It appears in sources from Greece and the Near East starting in the middle of the first millennium BCE, for example Herodotus, who describes it as beyond the Straits of Hercules (modern Gibraltar).

Roman authors tend to echo the earlier Greek sources, but from around the end of the millennium there are indications that the name Tartessos had fallen out of use, and the city may have been lost to flooding, though several authors attempt to identify it with cities of other names in the area.

Archaeological discoveries in the region have built up a picture of a more widespread culture, identified as Tartessian.The Tartessians were rich in metal.

In the 4th century BCE the historian Ephorus describes "a very prosperous market called Tartessos, with much tin carried by river, as well as gold and copper from Celtic lands".

Trade in tin was very lucrative in the Bronze Age, since it is an essential component of true bronze, and comparatively rare.

Herodotus refers to a king of Tartessos, Arganthonios, presumably named for his wealth in silver.The people from Tartessos became important trading partners of the Phoenicians, whose presence in Iberia dates from the 8th century BC, and who nearby built a harbor of their own, Gades (present-day Cádiz).