In ancient Rome, a series of majestic aqueducts brought water to the masses in a feat of architectural and engineering prowess that’s still visible in Europe today. But just how much water did those structures really bring to the city? Not as much as previously thought — LiveScience’s Tia Ghose reports that new research has shed light on the amount of water held by Rome’s “majestic” Anio Novus aqueduct.

The aqueduct, which began construction in the year 38, brought water nearly 90 miles from a river in the Apennine Mountains into Rome, helping the mighty city’s population to double, Ghose writes. But while it’s still heralded as an impressive engineering coup, it’s been hard for historians to figure out how much water the system brought to Rome.

Varying slopes, water speeds and scanty historical accounts made it hard to calculate the aqueduct’s capacity in the past, reports Ghose. A group of geologists and microbiologists recently decided to study something different — the travertine, or limestone buildup on the inside of the aqueduct. When they assessed the shape and thickness of the travertine, they concluded that the aqueduct usually was filled to the brim with water, on the order of 370 gallons of water per second.

Though that amount of water could have easily supplied the entire city with water, it’s still not as much as previously expected. In a statement, the scientists note that the very buildup which helped them solve a centuries-old mystery probably reduced the water flow by as much as 25 percent of the aqueducts’ original capacity.

Still, over 11 billion gallons of water a year is nothing to sniff at — at that rate, you could take 157 million standard 70-gallon baths a year.