Humayun's tomb, Delhi, India

This Picture of a hexagram is courtesy of Andy Mason from Flickr.
Humayun's tomb [(1605-1613] is known to have inspired the Taj Mahal and many later Mughal(Mogul)tombs.
There are a few explanations to the existence of this hexagram in the archway:
1. It is a Hindu symbol
2. It is a Mandala symbol
3. It is a Persian import