The Romans often attributed their success at building the greatest empire of the ancient world to various virtues of their own. However, it seems their faults also played a part, or perhaps just one fault running beneath Tiber Valley that prepared the ground for the eternal city.
Rome's astonishing empire would have been impossible without its geographic advantages, including a stable source of freshwater that could be crossed with ease. Before the population got large enough to put up extensive bridges, Tiber Island split the river so that each side could be crossed without needing to swim.
Geologists and archaeologists studying Rome's origins have found that the island came into existence because crustal movements shifted the course of the river soon after Rome was founded.
Long before this, Tibur valley was carved to such a considerable depth that if sea levels had been where they are today, the valley would have been flooded with salt water (ironic given Rome's subsequent practice of sowing their enemy's fields with salt). However, when Rome was founded, seas were low enough to not touch most of the valley. Deep layers of sediment carried by the river had built the valley back up to its present levels and formed Rome's foundations, Dr Laura Motta of the University of Michigan reports in PLOS One.
Drill cores taken around Rome reveal this build-up. Bouts of heavier rain explain most of the bursts of sedimentation the researchers found, but one required a different explanation.
“Suddenly, in the sixth century BCE, you see this dramatic increase in the sedimentation rate,” said Dr Andrea Brock in a statement. “In less than a century, nearly six meters [20 feet] of sediment were deposited in the river valley.”
Absence of similar signs elsewhere suggest this was not the consequence of temporary climate change. Variation in the ages of the sediment at the same depth confirmed something unusual was going on.
"This triggered some suspicion that there was a fault line that was displacing two sides of the valley," said Motta. After further research, the authors concluded that the fault displaced the valley walls and redirected the river, producing Tiber Island, which subsequently became sacred to the Romans as a place of healing.
Large earth movements reshaped the landscape to make it more suited to urbanization. The period matches when Rome moved from a small village to a site of major construction, and the cutting of stone upstream further promoted the deposition of material around the island and made the river even easier to cross.