The first dress rehearsal for the opening ceremony of the Beijing Olympic Games was held inside the National Stadium on Thursday.

But no one got a glimpse of what was going on inside the bird's nest because the rehearsal was held behind closed doors under tight security.

No one got a glimpse of what was going on inside the
bird's nest because the rehearsal was held behind
closed doors under tight security. (CCTV.com)

Three layers of fencing and an army of security guards on a 24 hour patrol encircled the Bird's Nest, with the gates to all the fences locked from the outside. This makes the Bird's Nest the heaviest protected area in the Olympic green.

In order to cater to the strict security of the opening ceremony, special features have been added to the construction near the National Stadium both from above and underground.

Construction workers making final touches on the Stadium roof that day all signed confidentiality agreements to keep the opening ceremony a surprise.