Nor' Loch was drained (creating land for today's Princes Street Gardens), and the Mound was constructed to provide a second, westerly access between the two settlements.
Nor Loch was drained because there was a drought.
mnli hypothesis: Nor Loch was drained because there was a drought. premise: Nor' Loch was drained (creating land for today's Princes Street Gardens), and the Mound was constructed to provide a second, westerly access between the two settlements.