Rolling Foundations

In order to withstand earthquakes most buildings in Japan are built on rolling foundations.  An initial foundation is put down, then rolling balls are placed on top, and then the building is built on a second foundation above the rollers.  This allows the rollers to move in an earthquake and absorb most of the vibrations, protecting the rest of the building.

I've understood this concept, but recently I got to actually see it.  There are two buildings under construction next door to us, and one day looking out the window I saw what looked like a bunch of white bubbles.  It took a minute to figure it out, but they're the rollers in the foundation.