How did Christmas start with?

Christmas has its origins in the belief that Jesus was born 9 months post the arrival of an angel to Mother Mary for telling about the birth of the Great Lord and it was believed to be held on 25 March. As a result, Christmas celebrations are devised from the late-night religious mass held to commemorate the big day and was tweaked to coincide closely with the winter solstice that is the biggest day of the season.
It is also believed that the day may also have been selected as it is the pagan Roman midwinter holiday that falls on winter solstice and as a result, it is termed as Saturnalian festival of Dies Natalia Solis Invicti that happened in December close to the date and Romans celebrated the event with much joy and happiness.