If you go to Lisbon and stand on the main square by the river, with the Tagus on your back, you’ll notice that that section of downtown, with its parallel post-earthquake streets, is between two hills: on the right, that of the castle and on the left that of the shopping area and the neighbourhood known as Bairro Alto, which translates as High District because it’s on the hill top. Downtown is literally down and, in Roman and pre-Roman times, it would have been largely flooded. To illustrate this, consider the following image where you can see the modern-day riverbank (red) and roughly where it was around two thousand years ago (dark blue), receiving water from two small streams (light blue):
What caused the riverbanks to change was a mixture of natural process and human action, with sand naturally accumulating along the shore, narrowing the watercourse, and growing urbanization along the river. However, this was a slow process and it was only in the Middle Ages that construction in today’s downtown picked up steam. During pre-Roman and Roman days, the Tagus would have stretched a navigable arm inland, determining both a natural western limit of the settlement and the location of its fish processing and trading areas. And from the first human inhabitants until the 13th century, Lisbon itself would pretty much be the castle hill alone. Suburban areas would start right on the other hill, crossed by a westwards road along which there would have been several villas (Guardado da Silva 2008, 49).
Finally, the second thing to take into account is the nature of the artefacts that indicate which gods were worshipped in pre-Christian Lisbon and where in the city. Most of the times, the evidence comes from inscriptions and ex-votos, but they were often used as construction material, especially in the Christian period, which means they may not have been found in their original location and, therefore, will be of limited use. When available, information about the original discovery and the text inscribed on the artefacts will be of great value.