Brick structures are built up by adding layer of bricks from the bottom, upwards. In this case the stonecutters had to work from top upwards.

The small box placed at the center of the stupa contained bodily remains such as teeth, bone or ashes of the Buddha or his followers, or things they used, as well as precious stones and coins. 
This box is known as a relic casket. It was covered with earth. Later, a layer of mud brick was added on top.
And then, the dome like structure was sometimes kings. covered with carved stone slabs.

The Ramayana contains the story of Hanumana and other monkeys. They promised to help Rama in his searching for Sita. Hanumana had special powers which enable him to reach Sri Lanka, in spite of many difficulties.
He found the whereabout of Sita, who was kept in Ashok Vatika by Ravana. He set Lanka on fire. He also brought Sanjivni herbs to treat Lakshaman. He remained with Rama.

In my state, Tulsidasa's Ramayana and Ved Vyasa's Mahabharara are popular. The version is in Hindi language.

(i) The word Stupa means a mound. There are several kinds of stupas, round and tall, big and small which can be found.
(ii) There is a small box known as a relic casket, placed at the centre or heart of the Stupa. This may contain bodily remains (such as teeth, bone or ashes) of Buddha or his followers or the things which they used, as well as precious stones and coins. This box was covered with earth. Later, a layer of mud brick or baked brick was added on top. And then, the dome like structure was sometimes covered with carved stone slabs.
(iii) Often, a path known as the Pradakshina Patha was laid around the Stupa. This was surrounded with railings.
(iv) Entrance to the path was through gateways. Devotees walked around the stupa in a clockwise direction, as a mark of devotion.
(v) Both railings and gateways were often decorated with sculptures.

(i)The stupa is located at Sanchi, Madhya Pradesh.
(ii)The brick mound was probably built at the time of Ashoka.
(iii)The railings and gateways were added during the time of later rulers.