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Robert de Beaumont (who was both Count Robert II of Meulan and the 1st Earl of Leicester, a close battle-companion of William the Conqueror in the Battle of Hastings, and something like a grand-nephew of St. Helvise) was a great lord, but he had no wife and he had no heirs. He had been supposed to be married to Godehildis, the daughter of his neighbor Seigneur Raoul II de Tosny, seigneur of Conches, a fellow battle-companion of William the Conqueror who was sometimes friend, sometimes ally, and sometimes enemy raider of Meulan.
But Raoul decided he’d rather marry his daughter to Baldwin, a younger son of Eustace, Count of Boulogne. If Godehildis and her children had lived, this would have been a good move, as Baldwin ended up becoming King Baldwin I of Jerusalem. But with none of their children alive, Godehildis accompanied her husband on the pilgrimage/First Crusade in 1096, fell ill at Marash, and died.
Meanwhile, Robert started looking around for a wife, but apparently not too quickly. He ended up finding someone, also not long before the First Crusade. He married Isabel de Vermandois, daughter of a younger son of the French king. They had to get a dispensation from the Pope to get married, because they were related within the seven degrees. They married in 1096, right before Isabel’s dad left on Crusade. (Possibly Isabel’s dad was getting his affairs in order and making sure his daughter was provided for. Possibly he needed traveling money.)
Robert was a good lord, very wise, but over 35. Isabel was young (12, the legal age then to get married). But the marriage probably wasn’t consummated until the usual consummation age for early marriages, which was 14.* France had a thing for preventing breakage of betrothals, by marrying people off and then just having them sit around and wait for years. (Though it obviously didn’t always work. Look at Godehildis.)
But at first it worked out. They had kids. Lots of kids. Three sons and six daughters would usually be regarded as a sign that a lady loved her lord and voluntarily spent a lot of time in his bed.
But after twenty years of good marriage, Robert was over 55 and Isabel was just middle-aged. Apparently midlife crises aren’t just a modern thing.
William de Warenne, 2nd Earl of Surrey, had been looking everywhere for a wife with royal blood. Isabel had it. He seduced and ran off with her in 1115 – legend says at a tournament, after impressing her. She started having kids with him even before they could get married.
Robert de Beaumont fell into a deep depression of shame and heartbreak. He couldn’t take care of business or his own kids. His local bishop tried to trick him into taking an interest in life, but it only semi-worked; Robert decided that he should do something constructive and took a monk’s habit in 1116. He died within a couple years, in 1118.
Isabel and William got married then, and had absolutely no shame about the whole thing. They had three sons and two daughters, and William married off one of the girls to a Scottish prince. Two of her sons became kings and she was the ancestress of the royal line there.
Isabel survived her second husband, too. She didn’t die until 1147 or 1148.
(Mind you, Robert probably wasn’t any saint. He did a lot of raiding and grabbing lands himself, and he was on that hunting party when King William Rufus had his “hunting accident.”)
* Medieval marriage and consummation ages varied A LOT. In general, most people knew that it was better to let girls grow up before starting with the babies, and that boys did better if they were older too. Medievals also wanted girls to have time to build a trousseau and skills (and a dowry or some kind of finances), and they wanted boys to be able to support a family.
OTOH, the more people were afraid of war or diseases carrying people off, the more urgent they were about marrying off their kids young. It was also a way of safeguarding your family line instead of somebody else’s, because marrying girls off at puberty keeps them from losing their virginity with other people than their husbands. (And boys’ parents had to worry about the financial and emotional drain of taking care of illegitimate kids. Even though it was common and it was proof their boys weren’t sterile, that didn’t mean people were necessarily happy about it; and unhappy illegitimate kids might just get revenge on the main family somehow.)
On the gripping hand, if money and food was short, people usually discouraged their kids from moving out and marrying until quite late. Middle-aged marriages are usually a sign that people feel poor and miserable. But paradoxically, they also show up in some merchant and trade families, because people are just too busy and marriage is a risk that you can’t budget for.
Normans were pretty much on the side of marrying ’em off young. They had plenty of food, but they were at war a lot with each other and the French and everybody else. With the Crusades coming on, there was probably a lot more social and emotional pressure on parents for their kids to marry and have kids right away – because parents were afraid they might lose the whole family.