Isabel of Bourbon: The Son Velázquez Painted on a Rearing Horse

She had lost every child born to her before him. As a little boy, her son was painted by Velázquez on a rearing horse, a command baton in his hand, to hang between the portraits of his parents. The family's future had been given a place on the wall.

Baltasar Carlos was born in Madrid on 17 October 1629, the son of Isabel of Bourbon and Philip IV of Spain. This time the child lived, and he was a boy. The court was ready to celebrate the arrival of its future king.

Isabel had come to Spain as a French princess in 1615. She was the daughter of Henry IV of France and Marie de' Medici, and her marriage belonged to a double arrangement between the two royal families. Her brother married Philip's sister; Isabel married Philip. The princesses crossed the frontier in opposite directions, each carrying her part of the agreement into another country. In Madrid, Isabel's French clothes were exchanged for Spanish ones. Even her appearance had to make the crossing.

The children began to arrive in 1621. The first daughter lived little more than a day. Another survived only weeks. One reached toddlerhood. None of the four was alive when Baltasar Carlos was born. Royal genealogies make short work of such lives, a name and two dates, sometimes scarcely any distance between them. For Isabel, they had occupied eight years of pregnancies, births and burials.

The court wanted a son. She had already lost four children.

On 4 November the new prince was baptised in the parish church of San Juan, beside the palace. The Countess of Olivares carried him in a chair of rock crystal, an infant surrounded by the splendour appropriate to what he was expected to become. That evening Madrid lit up with illuminations and fireworks. Orders went out to the monarchy's territories to celebrate the birth. A baby had arrived, and rejoicing was now official business.

When he was two, the prelates, nobles and cities of Castile swore allegiance to him as heir. There would be years of instruction before he could govern, but his subjects could begin their part considerably earlier. His future was being prepared for him.

Velázquez gave that future its most enduring shape. In the equestrian portrait, painted around 1635, Baltasar Carlos sits on a rearing horse beneath an open blue sky. A sash crosses his body. The baton and little sword belong to the language of command, the same language used in portraits of the grown men of his family. He is visibly a child, dressed for responsibilities that will have to wait.

The picture was intended for the Salón de Reinos at the Buen Retiro palace, above a doorway between the mounted portraits of Philip and Isabel. Around the hall were paintings of military victories and the labours of Hercules. Visitors could look from the king to his son and see the succession laid out for them. The boy had his own place among the claims the monarchy made about itself.

Isabel's place was becoming more substantial than a portrait might suggest. During Philip's absences on campaign in the 1640s, she exercised government in Madrid. The French princess brought across the frontier to marry and bear children was now governing while Spain fought the French. The work of preserving her son's inheritance included the business of keeping his father's monarchy functioning.

She was still governing when she became ill in September 1644. Philip was away at the Aragonese front. As her condition worsened, the sacred image of the Virgin of Atocha and the body of Saint Isidore were brought to her apartments. On 5 October she received the last rites.

Her two surviving children, Baltasar Carlos and his younger sister María Teresa, were kept out of the bedroom. Isabel would not have them exposed to infection. She died on 6 October, attended by women of her household and clergy. Philip was still in Aragon.

She had seen her son to within days of his fifteenth birthday. None of his elder sisters had lived to see a second.

For two more years his future continued to be prepared. He accompanied his father to Aragon, and a marriage was planned with his cousin Mariana of Austria. The child in the equestrian portrait was approaching the age at which the arrangements made around him would become his adult life.

In the autumn of 1646 he fell ill in Zaragoza. He died there on 9 October, sixteen years old, eight days before his seventeenth birthday. Isabel had been dead for just over two years.

The marriage arrangements survived him in a different form. Mariana, intended for the son, married the father in 1649. She was fourteen; he was forty-four. She was his niece as well as his second wife. The monarchy needed another legitimate male heir, and the young woman who had been chosen for its next king became the wife of its present one.

In the family group planned for the Salón de Reinos, Isabel had her son beside her and Philip had his successor. The little rider carried the equipment of command, with years still to grow into it. Of the three people represented there, he alone never wore a crown.