JIDDA, Saudi Arabia — Just off a desert road about an hour’s drive from this port city, an enormous arched gate capped by three domes rises out of the sand like the set for a 1920s silent film fantasy. It is, instead, a fantasy of contemporary urban planning, the site of what one day will be King Abdullah Economic City, a 65-square-mile development at the edge of the Red Sea. With a projected population of two million, the city is a Middle Eastern version of the “special economic zones” that have flourished in places like China.

The city is one of four being laid out on empty desert around this country, all scheduled for completion by 2030. They follow on the heels of the country’s first coeducational university, which opened last year next to the King Abdullah site, and a financial district nearly the size of Lower Manhattan that is rising on the outskirts of the capital, Riyadh.