“Secrets of the Dead” (7 p.m., PBS, check local listings) unearths one of the great mysteries of archaeology and Chinese history. “China’s Terracotta Warriors” opens up the tomb of a conqueror who died 200 years before the time of Christ, a man who united his country and who changed a way of life and death for his kingdom.

Qin Shi Huangdi would bring seven warring kingdoms together to form China’s kingdom and then anoint himself first emperor of China. As death neared, Qin commissioned an “army” of 8,000 clay soldiers to protect his tomb in the afterlife. Until Qin’s time, a ruler’s funeral would mean ritual slaughter for the entire royal entourage, as upwards of thousands of courtiers were required to accompany their master to the grave.

This “Secrets” speculates on what the clay soldiers looked like when first crafted and interred and shows them painted and fully armed for the first time on television. Archaeologists speculate on the technology required to create 8,000 soldiers in less than two years. One expert contends that the production may have resembled a kind of assembly line — beating Henry Ford’s Model T facility by more than 2,000 years.

Tonight’s other highlights

• The top five compete on “American Idol” (7 p.m., Fox).

• A decade before her stint as a singer/dancer on “30 Rock,” Jane Krakowski co-starred in the 1991 dance showcase “Stepping Out” (6 p.m., TCM) with Liza Minnelli.

• Claire and Gloria’s plan for a serene Mother’s Day run amok on “Modern Family” (8 p.m., ABC).

• “Nova” (8 p.m., PBS, check local listings) ventures to the ancient Andean city of Machu Picchu and recently discovered graves from the Incan era.

• “Custer’s Last Man: I Survived Little Bighorn” (8 p.m., History) explores new theories about the Battle of Little Bighorn in 1876.

• “MythBusters” (8 p.m., Discovery) evaluates theories about an ancient torpedo and puts a truck filled with wine to the test.

• A super saver tries to support two families via “Extreme Couponing” (8:30 p.m., TLC).

• A fan convention becomes a dangerous place for the cast of a remake of “The Goonies” on “Breaking In” (8:30 p.m., Fox).

• Cooper revisits a case from his past on “Criminal Minds: Suspect Behavior” (9 p.m., CBS).

• A troubled couple falls under suspicion after their baby is found abandoned on “Law & Order: Special Victims Unit” (9 p.m., NBC). Lori Singer guest stars.

• A bite from a rabid bat ruins a boy’s day on “I’m Alive” (9 p.m., Animal Planet).

Cult choice

Directed by Ridley Scott, the 1979 feature “Alien” (7 p.m., IFC) all but reinvented the science-fiction thriller.