According to the description found in the sixty-sixth Sarga of the Shrimad Valmiki Ramayana, in the morning, upon seeing the great sage Vishwamitra, Lord Rama, and Shri Lakshmana, King Janaka welcomed, honored, and worshipped them and said - "O great sage! You are most welcome. Kindly instruct me as to how I may serve you today."
Hearing the affectionate words of King Janaka, Sage Vishwamitra said - "O King! These are the supremely valiant Kshatriya sons of King Dasharatha, whose fame is spread throughout the entire world. They wish to see your great bow. Kindly show them that bow. Having beheld that divine bow, they will be satisfied and return to their capital."
Upon hearing this from Sage Vishwamitra, King Janaka said - "O revered sage! Please listen to the account related to this bow and the purpose for which it is kept here; I shall describe it accordingly. O Lord! The eldest son of King Nimi of Mithila was renowned as King Devarata. That noble Devarata received this bow as a sacred trust. After Lord Shiva had slain Tripurasura, the Gods handed over this bow to him.
It is said that in ancient times, during the destruction of Daksha Yajna, i.e., Daksha's sacrifice, the supremely powerful Lord Shiva, in a playful yet wrathful manner, lifted this bow and said to the Gods - 'O Gods! I desired a share in the sacrifice, but you did not grant me my portion. Therefore, I shall use this bow to sever all your heads.'
Hearing this, all the Gods became distressed and began to praise and appease Mahadeva. Ultimately, Lord Shiva was pleased by their prayers. Being pleased, Lord Shiva gave that divine bow back to the Gods. This is the same rare and divine bow of Lord Shiva, which the gods later entrusted to my ancestor King Devarata."
Thereafter, King Janaka again said - "O revered sage! In ancient times, one day, while I was ploughing the fields for the purpose of performing a Yajna and purifying the land, a divine and extraordinary girl emerged from the furrow created by the plough. The ploughed land is called Sita, and since that girl was born from the furrow drawn by the plough, she was named Sita. My daughter Sita, who manifested from the earth, in due course grew into an extremely beautiful, virtuous, devoted, and righteous young woman. I had resolved regarding my Ayonija daughter that whoever, by his strength and valor, would string this bow, only he would be worthy of marrying Her.
Thus, I raised my extremely valiant daughter. O revered sage! Many kings approached me seeking the hand of my daughter Sita, who was born from the earth and continued to grow in beauty and virtue. However, I told those kings that my daughter is Viryashulka, meaning only a man who demonstrates proper valor would be worthy of marrying Her. This is why I have not yet given Her hand in marriage."
Thereafter, after learning the glory of Shiva's bow from King Janaka, Lord Shri Rama broke the bow in Sita Swayamvara and accepted Goddess Sita as His bride.
॥Thus concludes the Shri Janaki Janma Katha described in the Shrimad Valmiki Ramayana॥