This is the G string on the violin. It's the lowest string on the violin. And that's actually the lowest note you can play on the violin.
One of my favorite pieces that starts on the G string, nice and strong, is called Zigeunerweisen by Sarasate.
It's nice and powerful, the G string. Here's another example, Franck's Sonata. That's the G string on the violin, nice and powerful.