Marriage
Most girls married young - at fifteen or sixteen, or younger. They married the men their fathers chose. For marriage, at least to the rich, was business. Only the really poor married for love.
It cost a man money to feed and clothe a daughter. When she got married, her husband took on the job of keeping her. So her father paid the bridegroom some money or gave him a present. This was the dowry. All but the very poor paid dowries. Tradesmen might give some furniture and cooking pots. Kings and great lords paid vast sums.
A marriage, and the payment of a dowry, was a deal between two families. If the fathers were kings, it might be part of a peace treaty. If they were merchants, it was a piece of business. The young people's wishes had nothing to do with it.
Heiresses were special. They were girls who had no brothers. When their fathers died, they (and their husbands) got the land or money. Many men dreamed of marrying a rich heiress. To a king, marrying an heiress was as good as winning a war. Henry II of England became ruler of all of south-west France when he married Eleanor of Aquitaine.
Walter Robson: Medieval Britain; Oxford University Press, 1991/2000, page 88