Archaeologists in Spain have discovered a possible hidden Roman Empire from over 2,000 years ago.

A team of researchers from the University of Cádiz started exploring an area of the Sierra de Cádiz region last year hoping to just find a few remnants of ancient life there.

Instead, they were stunned to come across 57 Roman Empire-era sites — which they believe could all be connected, based on trade and communication routes, according to the Independent.

Now, they are looking more closely at how the sites are linked, which is the first time ancient Roman settlements there have been thoroughly analyzed.

“The objective is to know the interaction of the Bay of Cadiz with the settlement of the Guadalete River depression during the Roman period, an aspect practically unknown until now,’ the researchers said in a report.

The settlements, which are in areas around Arcos de la Frontera, Bornos, Villamartin and Puerto Serrano, would have all been interconnected by the Guadalete River in the Spanish province of Cádiz, which leads researchers to believe they were part of a hidden empire, the Independent noted.

The Romans settled around the Guadalete River after they conquered Spain in 264 BC.