King Alfred didn't do much with the place until the Vikings became a problem; he fortified it, making it therefore usable by others such as King Ecgberht of Wessex (ruled 802-839), and King Edgar (ruled 959-975). It was abandoned when Svein Forkbeard invaded in 1003.
Always treated as a potential defensive position more than an important municipal center, the hill was crowned with a motte-and-bailey three years after the Norman Conquest. Topographical limits kept the town small and cramped, although not so small that William the Conqueror couldn't gather all his nobles, prelates, and sheriffs to take the Oath of Salisbury, declaring loyalty to him and no other. It is likely that this occasion saw William presented with the completed survey called the Domesday Book.
Why was it called the Oath of Salisbury if the town was called Old Sarum? The Domesday Book calls it Sarisburie (from Old English Searesbyrig, "Seares fortress"). Sarisburie was often abbreviated to Sar̅, but the -r̅ was often used to abbreviate words ending in -um. Sometime in the 1200s the place started being called Sarum. Meanwhile, the Medieval Latin Sarisburie was corrupted to have an -l- in the middle. Sarum had the "Old" tacked on to distinguish it from the new town b being built near the new Salisbury Cathedral. Modern Salisbury can also be rightly called "New Sarum."
The aerial photo above shows the excavated motte-and-bailey structure at the center of the walled town. You can see the old Salisbury Cathedral foundation. For scale, the length of the Norman cathedral was 185 feet, smaller than most of its era.
Henry II had his wife, Eleanor of Aquitaine, kept at Old Sarum. Their son Richard the Lionhearted designated a plain near there for tournaments.
William of Malmesbury called Sarum "more like a castle than city, being environed with a high wall"; he certainly drew from firsthand experience, since he became a good friend of Roger, Bishop of Salisbury, who owned the land on which Malmesbury Abbey was situated, where William spent his entire adult life. William noted that the site did not have sufficient water to make it sustainable, and supposedly this was one reason why a new cathedral needed to be relocated. Peter of Blois, canon of the cathedral, described it as "barren, dry, and solitary, exposed to the rage of the wind"; a papal legate looking into the cathedral verified that the wind was so strong that divine office could sometimes barely be heard.
Once the "new" Salisbury was established, Old Sarum lost population and significance—and materials, as resources were dismantled to take to the new town. Edward II had the castle demolished in 1322. Old Sarum was one of the first sites named in the 1882 Ancient Monuments Protection Act.
Peter of Blois had very strong feelings about Old Sarum. He felt that the cathedral in Old Sarum was "as a captive on the hill where it was built, like the ark of God shut up in the profane house of Baal." Let's take a look at this colorful canon next time.