Architectural design isn’t everything, it appears that their concrete “recipe” was in fact different:
“University of Utah geologist Marie Jackson… and her colleagues have found that seawater filtering through the concrete leads to the growth of interlocking minerals that lend the concrete added cohesion.” http://unews.utah.edu/roman-concrete/
“University of Utah geologist Marie Jackson… and her colleagues have found that seawater filtering through the concrete leads to the growth of interlocking minerals that lend the concrete added cohesion.” http://unews.utah.edu/roman-concrete/
includes some tasty microscopic photography