I want to know the answer to the following question:
What castle was built at a strategic point?
All the background I'm provided with is that "Feudal levies could only be raised for a fixed length of time before they returned home, forcing an end to a campaign; mercenary forces, often called Brabançons after the Duchy of Brabant but actually recruited from across northern Europe, could operate all year long and provide a commander with more strategic options to pursue a campaign, but cost much more than equivalent feudal forces.". Is that enough to answer the question?
Answer: no