So, the obvious question is: what did Vanbrugh and the Earl of Carlisle think they were doing in constructing a line of medieval fortifications at the entrance to the estate ?

It is not as if there was an enemy to keep out. They are surprisingly serious, proper fortifications, not a piece of eighteenth-century game playing or ornament.

Of course, Lord Carlisle had been Earl Marshal. And Vanbrugh was a herald. In some way, it must be associated with Carlisle’s interest in his lineage, not least because they are accompanied by a pyramid dedicated to the memory of his ancestor, Lord William Howard. But no-one at the time thought it particularly unusual, apart from Horace Walpole and he described it in the 1770s:-