Here, the arch bridge has a number of segments. Arrange the segments to create a temporary arch bridge. Walk over the bridge to check its stability.

What did you observe? 
Although the arch bridge is not concreted or contain anchorage, it possesses the stability even after loading it.

The science behind it :
Arch shape structures have more stability than any other shape. The entire load applied over the arch shape is transferred to the ends thereby giving the stability to the structure.