A lot of people imagine a castle as being built, and then just staying put until it becomes a ruin, but for a place like Alnwick, which has had quite an eventful life (as castles go) and has gone from a Norman border fortress to a home for the Duke and Duchess of Northumberland, it has evolved almost continuously over a period of nearly 1000 years.
We know there was definitely a castle at Alnwick by the year 1138, because that’s the first record of a strong, well-protected fortress being here (current theory suggests it dates as far back as the very early 1100s). But there is very little of that castle remaining – if you go to the State Rooms or the Dungeon on your visit to Alnwick, the archway you walk under to get there is, essentially, the Norman bit.
Is a castle only as old as its oldest feature? Maybe – but most of the characteristic features of Alnwick, like the two ‘Octagonal’ turrets on either side of the drawbridge, or the Barbican gatehouse (the gory medieval entrance to the castle) are much more recent: one is from the mid-1300s, the other was finished in 1475. So maybe you could say the castle is as old as the family that have lived here for over 700 years?
Then again, by the 1700s Alnwick was almost a ruin, but was completely restored by the 1st Duke and Duchess of Northumberland in the 1750s and 1760s ... and then restored again in the 1850s and 1860s by their grandson, the 4th Duke – so maybe it’s more of a Georgian or a Victorian castle? Much of the Inner Courtyard, and the tower housing the Library, are only 150 years old.
And even now, pieces of wall are being taken out and replaced by brand new twenty-first century stone by the on-site stonemasons – so certain elements of the Clock Tower and Constable’s Tower, to name just two, are only a few years old!
So, when Alnwick Castle is so many different ages at the same time, my answer to the question is simply that there’s been a Castle on this spot for around 900 years... after all, age is only relative, isn’t it?