In this excerpt from "Bitter Rivals: Iran and Saudi Arabia," correspondent Martin Smith reports from inside regime-held areas of Syria on the conflict’s roots — and explores how Iran’s support for Bashar al-Assad has helped fuel one of the most brutal wars in modern times. Subscribe on YouTube: bit.ly/1BycsJW The two-part FRONTLINE series "Bitter Rivals: Iran and Saudi Arabia" tells the epic, inside story of a dangerous feud that has plunged the Middle East into unprecedented levels of violence — with exclusive, on-the-ground reporting from inside both countries as well as Yemen, Iraq, Pakistan, Syria, and Lebanon. Part one of "Bitter Rivals: Iran and Saudi Arabia" is now streaming: to.pbs.org/2FXi9b6 Part two premieres Tues., Feb. 27 at 10/9c on PBS & online: to.pbs.org/2FXi9b6 Twitter: twitter.com/frontlinepbs Facebook: www.facebook.com/frontline Google+: plus.google.com/+frontline/posts FRONTLINE is streaming more than 200 documentaries online, for free, here: to.pbs.org/hxRvQP FRONTLINE is made possible by PBS and CPB. Major support is provided by The John D. and Catherine T. MacArthur Foundation. Additional funding is provided by the Ford Foundation, the Park Foundation, The John and Helen Glessner Family Trust, the Heising-Simons Foundation, Wyncote Foundation, and the FRONTLINE Journalism Fund with major support from Jon and Jo Ann Hagler on behalf of the Jon L. Hagler Foundation. Major support for "Bitter Rivals: Iran and Saudi Arabia" is provided by the Corporation for Public Broadcasting, with additional support from the Henry Luce Foundation’s Initiative on Religion in International Affairs and The Pew Charitable Trusts.