Today (Sept. 11) marks the 10th anniversary of the 9/11 terror attacks that claimed the lives of thousands of innocent civilians in New York, Washington D.C. and Shanksville, Pa. The anniversary offers a time for people to reflect on that harrowing day, and rock acts such as Guns N' Roses, Nikki Sixx, Slash, Rev Theory, Tommy Lee, Tom Morello and others have shared their thought on the day via Twitter. Here's a look at what some from the world of hard rock are tweeting about the 10 year anniversary of 9/11: