It’s easy to take all the hard work that goes into bridge-building for granted. In order for cars to pass safely over the water beneath, engineers employ some clever construction tricks to make these technical marvels a reality.

In the video from the Minnesota Department of Transportation above, you can watch time-lapse footage of a new bridge being constructed above the St. Croix River. The work that takes place above the surface is mesmerizing to witness, but before any of that can happen, crucial steps are taken 150 feet below the water.

Business Insider also produced their own version of the video, using graphics to illustrate how exactly the bridge's foundation was laid. After drilling watertight chambers deep into the ground, a box-shaped dam was constructed around them, allowing columns to be built stretching up from the riverbed to the water’s surface.

Bridge engineers have been using similar construction techniques for over a century, and they’ve helped to make older structures like the Brooklyn Bridge stable enough to be used to this day. St. Croix Crossing will connect Oak Park Heights, Minnesota to St. Joseph, Wisconsin, and is scheduled to be completed by fall of this year.

Banner image courtesy of MnDOT.

[h/t Business Insider]