In May the British flotilla entered Lake Champlain from the Sorel River, and cruised, May 9, as far southward as Otter Creek, terrifying Vermont for the safety of the American flotilla under Lieutenant Thomas Macdonough at Vergennes. Irritated and alarmed by this demonstration, Armstrong ordered Izard to seize and fortify Rouse’s Point, or the mouth of Lacolle River, or Ash Island, and so close the entrance to the Lake.[150] Apparently Armstrong gave the order in ignorance that Lacolle River and Ash Island were strongly fortified British positions,[151] and that a battery established at Rouse’s Point, in the relative situation of forces, must have fallen into British hands. On this point the opinion of Izard was more valuable than that of Armstrong; and Izard, after much study and inquiry, decided to erect his fortifications at Plattsburg. He preferred the task of taking a position which he could certainly hold, although it would not prevent the enemy from passing if they chose to leave it behind them. At Plattsburg, therefore, he collected his troops, amounting to five or six thousand men, and constructed strong forts, while Macdonough’s fleet took position in the bay. While thus occupied, Izard cast anxious glances westward, doubting whether, in case of a reverse at Niagara or Sackett’s Harbor, he ought not to move on the St. Lawrence and threaten the British communications between Montreal and Kingston.[152] The same idea occurred to Armstrong, who in a letter dated July 27 recommended Izard to carry it out.[153] The letter reached Izard August 10, when he had advanced with his army to Chazy, and had learned enough of the concentration of British troops in his front to be assured that they meant to direct their serious attack against Lake Champlain. He wrote Armstrong a letter, August 11, which failed only in saying too little, rather than too much, of the dangers risked in obeying Armstrong’s order:[154]-- “I will make the movement you direct, if possible; but I shall do it with the apprehension of risking the force under my command, and with the certainty that everything in this vicinity but the lately erected works at Plattsburg and Cumberland Head will in less than three days after my departure be in the possession of the enemy. He is in force superior to mine in my front; he daily threatens an attack on my position at Champlain; we are in hourly expectation of a serious conflict. That he has not attacked us before this time is attributable to caution on his part, from exaggerated reports of our numbers, and from his expectation of reinforcements.... It has always been my conviction that the numerical force of the enemy has been under-rated. I believe this to be the strong point of our frontier for either attack or defence, and I know that a British force has been kept in check in Lower Canada for many weeks past, greatly superior to that which I could oppose to it.”