Local viewers of Discovery and National Geographic will appreciate that these channels which originate from the United States do have an eye on the region not just as a market but as a subject for programming. Tonight, China's most obvious wonder is featured in Secrets Of The Great Wall (Discovery, 8pm), beginning the channel's On The Inside series that looks behind the scenes at some of the world's natural and man-made wonders. But the wall (pictured) is still analysed through Western eyes, with Gulf War commander General Norman Schwartzkopf the man chosen to enlighten us as to the military role and impact of this structure, which does not only look amazing as it snakes across the country but revolutionised warfare and pushed architectural and military technology to the limit. To build what were apparently three walls, the Chinese invented bricks and mortar whose strength and durability have yet to be surpassed. And to defend them they invented crossbows, iron swords, cannons, hand grenades and mines, as well as a smoke signal communication system. But we are also reminded that the wall was built at huge human cost, and with little concern for lives lost. Experts of the Chinese Great Wall Society say one worker died for every metre completed. The economic cost, estimated at close to HK$3 trillion at today's prices, was also crippling. Discovery has also launched a fascinating series on Asian art, Artifacts (Sundays, 8pm), written and produced in the region. Tomorrow's episode, A Brush With Wisdom, looks at the development of calligraphy and Chinese painting, re-enacting the lives of famous artists and explaining the philosophies behind their work. National Geographic has also turned its attention to a culture in our midst, last Sunday profiling the Hakka people. The BBC's imaginative focus on time continues with The Time Lords (BBC World, 9.10pm). In this quirky documentary we learn that time travel is not just the stuff of science fiction but already exists, and that we do it every time we take off in a jumbo jet. Time traveller Kip Thorne boards a plane with an atomic clock to measure how far British Airways can take him into the future. Apparently, it is only the lack of cash for big enough engines that stops people travelling years into the future. But who, one wonders, has the time for such a journey?