From Command and Conquer Wiki

The Tiber (Italian Tevere, Latin Tiberis) was the third-longest river in Italy, rising in the Apennine mountains of Tuscany and flowing 406 kilometres (252 miles) through Umbria and Lazio to the Tyrrhenian Sea. It drained a basin estimated at 18,000 km² (6845 square miles). The river has achieved lasting fame as the main watercourse of the city of Rome, founded on its eastern banks.

It was near this river that the first tiberium meteorite hit and the first field appeared, destroying an olive plantation. It is unclear who discovered the crystal first, as the claims were put forward by both Kane and Ignatio Moebius. Regardless, the tiberium spread unnoticed and eventually managed to overrun central Italy, turning it into a devastated red zone. Gigantic tiberium glaciers occupy the site of Rome nowadays, with most of the city obliterated by the spread of tiberium. The air is saturated with tiberium vapor and has a greenish hue. The sky is overcast with tiberium gas clouds. The blue Tiberium also infested and turned the river into a near-unlimited blue Tiberium field.

No human settlements, except for a few mutant hovels exist in this area, though the high Tiberium concentrations led to the Scrin constructing their Relay Node where the Tiberian Age began. Nod, GDI, and Scrin forces fought out the final battles of the Third Tiberium War at or near ground zero.