Cholula, Mexico was second only to the Aztec capital Tenochtitlan (modern Mexico City), possibly with a population of up to 100,000. The great city stood at the foot of what appears to be an earthen hill that is, in fact, the largest pyramid ever built, covering over 46 acres and spanning an incredible 405 meters on each side! In addition to this great construction dedicated to Quetzalcoatl, the city had a reported 365 temples.
After taking the city during the Spanish Conquest, Hernan Cortes vowed that it would be rebuilt with a Christian church to replace each of the old pagan temples; less than 50 new churches were actually built, but the Spanish colonial churches are unusually numerous for a city of its size. Cholula is actually divided into eighteen neighborhoods or barrios, each with a patron saint. (source)
San Luis Potosi is another amazing city in Mexico with a Spanish-style to it.