The Island of Cape Breton is like a hand with its fingers stuck out in the sea. The very tip of a long promontory commanding one of the southern arms of the sea was chosen for the fort that was to be the strongest in all America. On three sides were the sea, with outlying islands suitable for powerful batteries and a harbor entrance that was both narrow and deep. To the rear was impassable muskeg--quaking moss above water-soaked bog. Two weaknesses only had the fort. There were hills to right and left from which an enemy might pour destruction inside the walls, but the royal engineers of France depended on the outlying island batteries preventing any enemy gaining possession of these hills. By 1720 walls thirty-six feet thick had encircled {215} an area of over one hundred acres. Outside the rear wall had been excavated a ditch forty feet deep and eighty wide. Bristling from the six bastions of the walls were more than one hundred and eighty heavy cannon. Besides the two batteries commanding the entrance to the harbor was an outer Royal Battery of forty cannon directly across the water from the fort, on the next finger of the island. Twenty years was the fort in building, costing what in those days was regarded as an enormous sum of money,--equal to $10,000,000. Such was Louisburg, impregnable as far as human foresight could judge,--the refuge of corsairs that preyed on Boston commerce; the haven of the schemers who intrigued to wean away the Acadians from English rule, the guardian sentinel of all approach to the St. Lawrence. "It would be well," wrote the King the very next year after the treaty was signed, "to attract the Acadians to Cape Breton, but act with caution." And now twenty years had passed. Some Acadians had gone to Cape Breton and others to Prince Edward Island; but statecraft judged the simple Acadian farmer would be more useful where he was,--on the spot in Acadia, ready to rebel when open war would give the French of Louisburg a chance to invade.