The battlefield was basically a narrow strip of land between the River Ouse and the cliffs of Hastings. The English held the western end of the hill, the right flank, with their longbowmen and infantry; the Normans had the eastern slope and the centre. The French knights were pushed into the centre by the Norman cavalry, and the tide of the tide was controlled by the river – the Normans could not cross it easily, so they kept the centre tight. In the final phases the English broke the Norman centre at the high point, and then the French left was left exposed. It’s a lesson in how a seemingly small geographic feature can dictate every manoeuvre; even the slightest hill or the curve of a river can decide a whole campaign. If you’re writing a chapter on it, keep a close eye on the exact distances and the angle of the hill, those are the numbers that make the story believable.

You might want to pin down the weather too – a mild breeze made the English arrows travel farther, while the Norman archers didn’t have as much range. Also note that the French knights were arranged in a tight column; the Norman cavalry broke that column on the hilltop, so the French got pinched from the sides. And don’t forget the importance of the “longbow” discipline – the English could fire a volley every few seconds, which kept the Norman centre from getting any breathing room. Those little details really make the scene feel authentic.

Sounds good. Just remember that the English had the high ground for a good part of the day, so their arrows cut the air and the French cavalry had to fight uphill – that small advantage can change the whole balance. Once you’ve locked that in, the rest will follow naturally.