What project became a safe route for travelers and protected China's northern
boarders? *

The Great Wall of China

Explanation:

The Great Wall of China was a fortification project that was first conceptualized and constructed in the 3rd century BC by the Emperor  Qin Shi Huang.

The idea was to protect the Empire's norther borders from the tribal warring people who were continuously attacking and harassing Chinese citizens, villages etc.

The project was a success and brought relative peace and safety in China's northern borders. Subsequent Emperors continued the development of the wall until as recently as the 17th Century under Ming Dynasty. During their time, the wall was so large it was recognized as the largest military and deference construction in the world.

more than 1 person for sure

those sounds of the natural world are bioacoustics, and they're more than a false-color spectrogram of data from the musiamunat conservation area.