Some of the most imposing structures ever built, medieval castles withstood both bloody assaults and the test of time. Designed like machines with nearly every architectural detail devoted to defense, castles represented the perfect fusion of form and function. Journey back to that unruly era as we examine the complexity of their construction and the multi-purpose they served--homes to kings and nobles, economic centers, courthouses, treasuries, prisons, and torture chambers.

It's the longest, most expensive and complicated railroad ever built. Ordered by the Czar in an effort to save his empire and unify his country at the twilight of the 19th century, the Trans-Siberian Railroad nearly tore Russia apart. Intended in part for defense, the railroad provoked a war, crossed great lengths over treacherous terrain, and encountered logistical and economic failures. Ironically, enemies of the state built the railroad--men sentenced to hard labor in Siberian prisons.

Booby traps continue to worry law enforcement.

The 1,522-mile-long Alaskan Highway takes 11,000 soldiers to build.

One of the longest suspension bridges in the world connects upper and lower peninsulas of Michigan.

44min | Aired on Mar 05, 2003 | TV-G | CC

Trains capable of speeds of up to 190 miles per hour can be found throughout the world.

44min | Aired on Mar 11, 2003 | TV-PG | CC

Made up of soldiers and civilians, scientists and specialists in an enormous variety of fields, the US Army Corps of Engineers was created over 200 years ago by Congressional mandate to respond, in peace and war, to the nation's engineering needs.

44min | Aired on Mar 18, 2003 | TV-PG | CC

A medical doctor who specializes in victims of torture explains its use.

The exterminator is man's last defense against pesky critters and creepy crawlers. Trace the history of this noble occupation from its humble beginnings, to its importance during the Black Plague, all the way to today's high-tech and ecologically sensitive pest-control experts.

45min | Aired on Jun 03, 2003 | TV-PG | CC

Hazardous-material shipment; classified government materials.

The controversial logging industry topples 4 billion trees annually.

For decades, the sound barrier loomed as an impenetrable wall against manned flight that buffeted planes with shock waves as they approached the speed of sound. Scientists thought the barrier couldn't be breached--until the development of jet technology and rocket fuel at the end of WWII.

45min | Aired on Jul 16, 2003 | TV-PG | CC

Witness the construction of a terrorist-proof safe room. Discover how your windows might someday act as biological weapons detectors. Learn how scientists are protecting the food you eat and water you drink. In the biggest technological push since the space race, inventors are creating cutting-edge devices, gadgets, and gizmos to keep you and your family--and even your pets--safe. Find out what technology can do to protect you, and how you can use technology to protect yourself.

44min | Aired on Jul 29, 2003 | TV-PG | CC

Military planners move soldiers and cargo halfway around the world.

45min | Aired on Aug 06, 2003 | TV-PG | CC

Terror Tech: Defending The Highrise

44min | Aired on Aug 12, 2003 | TV-PG | CC

In 1841 a conical bullet changes ammunition forever.

43min | Aired on Aug 13, 2003 | TV-PG V | CC

From soaring skyscrapers and sturdy bridges to jet planes and rockets, metals play a key role in every aspect of our world, and have done so ever since man first thrust copper into a fire to forge a tool.

46min | Aired on Aug 19, 2003 | TV-PG | CC

The Overseas Highway contains 51 bridges, linking mainland Florida with the Florida Keys.

The engineering marvel Machu Picchu, originally built by the Incas.

Two ribbons of concrete span the largest inland body of water in Louisiana and serve as the world's longest automobile bridge. Find out how this engineering marvel was conceived and completed.

44min | Aired on Oct 15, 2003 | TV-PG | CC

Tracing the history and predicting the future of shipyards.

Jet truck; mobile command truck; building specialty trucks.

Technology of sports captures the public's imagination and revolutionizes the sporting industry.

Dreamers and schemers try an odd assortment of flawed ideas for inventions.

44min | Aired on Dec 10, 2003 | TV-PG | CC

Super Soaker water gun; Lionel electric train; Erector set; cap gun.