Sea-Tac International Airport has expanded well beyond its original scope when it opened 70 years ago. 

When it originally opened, Sea-Tac had four runways. The original terminal cost $3.2 million to build. 

The first runways were built between 1943 and 1944. They were constructed in an "X" configuration to cover all wind conditions - It is the reason for the main terminal's shape. 

Service began with Northwest and United airlines. 

The airport was serving about 1 million passengers by 1954.

Today, Sea-Tac is ranked as the eighth busiest U.S. airport, serving nearly 50 million passengers in 2018. 

Also see | Sea-Tac Airport wait times may spike with new arrivals facility, senators warn

This summer, the Port of Seattle said it expects to handle about 170,000 passengers per day. While that sounds like blistering growth, the rate of growth has actually slowed to a projected 4% this year and perhaps 3% next year. It was as high as 12.9% in 2015.  

The port has some 100 projects in the works, or in planning, to cope with that growth. Those projects include expansion and upgrades to the north satellite, known as NorthStar, and a new International Arrivals Facility, which includes a giant sky bridge. The sky bridge is due to be complete later this year, which will connect the IAF to the south satellite, where planes will actually park. That sky bridge will be high enough to clear a 747. 

This year is expected to be the airport's busiest yet. Projected passengers are expected to surpass more than 50 million. 

Also see | Sea-Tac Airport opens new terminal to catch up with rapid growth