Chaukhandi Stupa-National Monument

Chaukhandi Stupa, present in Sarnath is a Buddhist Stupa located near 8 km from cantonment railway station Varanasi, Uttar Pradesh

And

ASI (Archeological Survey of India)

has declared it a National monument

It was basically built to mark the place where Bhagwan Budh met his first five disciples who are also known as

PANCHAVARGIYA BHIKSHUS

who deserted Bhagwan Budh when he had not attained Bodh Gayan.

They were actually used to be his friend who supported him for 6 years during self-mortification.
And

When Bhagwan Budh realizes that making suffer his body he won’t gain anything his friends don’t support his views and left him.

After seeing what he has attained they followed him and together made union known as
SANGHA

with this, the three gems of Buddhism formed

Buddha

Dhamma

Sangha

It is so called Chaukhandi because of its four-armed plan

it was originally constructed in 5th century AD

Hiuen Tsang, a traveller from China has also mentioned it in 7th century AD