Once and future king

Those who believe King Arthur was an early incarnation of Harry Potter may be disappointed by the second-season premiere of “Sacred Sites,” but the documentary uncovers some fact-based revelations that are nearly as mind-blowing as someone yanking a sword out of a stone. Upcoming episodes will spoil bedtime stories about the Maltese, Nazis and Egyptian priestesses.

7 p.m., Smithsonian

Inside the Islamic Republic

The latest edition of “Frontline” is so ambitious it takes four hours to unspool. “Our Man in Tehran,” which continues Tuesday, follows Thomas Erdbrink, the New York Times’ bureau chief in Iran, as he makes his rounds in the capital city, including a visit to an AA meeting.

9 p.m., TPT, Ch. 2

Get happy

Local wit John Moe kicks off the third season of his podcast “The Hilarious World of Depression” with Andrew Zimmern, who talks openly about his own struggles with addiction and depression. Guests in upcoming episodes of the American Public Media series include singer Neko Case and “Kids in the Hall” cast member Scott Thompson.

Now streaming via podcast

Neal Justin