Once upon a time, in the city of Mithila, there was a beautiful and virtuous daughter of King Janaka named Sita. When Sita came of age, King Janaka organized a Swayamvara for her. In the Swayamvara, Sita was given the right to choose her own groom.
King Janaka announced that whoever could lift and string the bow of Lord Shiva would be able to marry Sita. The bow was very heavy and powerful, making it impossible for anyone to lift it. Many kings and warriors came to the Swayamvara and tried, but none could lift the bow.
Meanwhile, Lord Rama, the son of King Dasharatha of Ayodhya, arrived there with his guru, Vishwamitra. At the command of Guru Vishwamitra, Lord Rama attempted to lift the bow. With great patience and strength, he lifted the bow and strung it. As soon as he did this, the bow broke.
King Janaka was very pleased and gave Sita in marriage to Lord Rama. Alongside this, King Janaka arranged the marriage of Lakshmana with Urmila, Bharata with Mandavi, and Shatrughna with Shrutakirti. All the marriages were celebrated with great pomp and grandeur. Thus, all three of Sita's sisters were married to Lord Rama's three brothers.