I recently visited Sarnath but the museum where the lion capital doesn’t allow photography so posting some pics from net of Ashoka Capital from Sarnath.
The Buddha was born into the Shakya or lion clan. The lion, in many cultures, also indicates royalty or leadership. The Lion is, a symbol of sovereignty.
Why back to back ?
A group of four lions joined back to back symbolizes a group of four things of equal importance:
Four Noble Truths of Buddha
And Four lions, looking in four directions and topped by the Chakra signify the spread of Buddha’s teaching all over the world.
The base of the capital has four animals, interspersed by the Chakra. They are bull, horse, elephant & lion, each representing one quarter. The Chakra signifies the spread of Buddhism.
We get elephant capital, single lion capital and bull capital from sites Sankisa, Vaishali and Rampurwa respectively. And a larger numbers of Ashokan pillars have been explored in pieces where capital is missing, such two pillars we get even at Delhi.
This last photo is from Sanchi (1st century). Even then Buddha was shown by symbols – a riderless horse, an elevated Aasan or a Chakra.