An excavation under the Gran Hotel Barcino in the historic downtown of Barcelona has uncovered a section of monumental pavement from the Roman towns forum that is unprecedented in its age, scale and state of preservation. The discovery rewrites the previous understanding of the orientation of the forum and how it aligned to the ancient citys main thoroughfares.The key find is a stretch of pavement made of slabs of Montjuc stone (rock extracted from the Montjuc mountain that overlooks Barcelona and has been the source of building material and infrastructure for the area since the pre-Roman Iron Age). It dates to between 15 and 10 B.C., the earliest founding years of the Roman city. It is made of precisely cut rectangular blocks, the largest of which are 1.48 long by 1.18 meters wide (approximately 5 by 4 feet). They are incredibly thick too, with the biggest being 35 cm, almost 14 inches thick. The slimmest was a heft 18 cm (seven inches). The variance made allowances for the uneven terrain and ensured the pavement was stable and flat. The surviving section covers 42 square meters (452 square feet).The area between the Bess and Llobregat river deltas has been populated since the prehistoric times. The Iberian Laietani people had several settlements on the site of what is now Barcelona, and when the Romans arrived in 15 B.C., they conquered the Laietani and founded the colony of Julia Augusta Faventia Paterna Barcino.The town was built with the typical urban design of a Roman city: two main streets the decumanus and the cardus intersecting in the center where the forum was located. It was encircled by defensive walls built between the 1st and 2nd centuries and the two main streets ended at four gates in the walls. The decumanus ran east to west, from the Porta Praetoria (west) to the Porta Decumana. The cardus ran north to south from the Porta Sinistra (north) to the Porta Dextra (south).The monumental pavement discovered under the hotel is parallel to the decumanus and perpendicular to the cardus.Until now, historians believed that the citys forum, the civic and administrative heart of Roman life, was aligned with the cardo.Archaeologists now say the forum was aligned parallel to the decumanus, running from sea to mountain.For years, we thought the Roman forum ran through the area of the Palau de la Generalitat, Maese explained. Now we see that it turns 90 degrees from being parallel to the sea to being perpendicular.Both the Catalan government and Barcelona City Council have accepted the revised interpretation and plan to update the citys museum displays accordingly.As for the ancient pavement, it will remain in situ. The hotel plans to incorporate the Roman remains found in the excavation into the breakfast room. It will not be open to the public, just to the fortunate hotel guests, but guided tours will be offered on special occasions in coordination with the Barcelona City Council.