But at the time the fort was built the bend in the river reached much farther toward the north. In later years the south bank was partially dredged away, and the bend was therefore considerably lessened. Thus the site of the fort, being close to the river bank, was some distance farther north than the building upon which the tablet is placed; in fact, the northern portion of the fort extended over ground now covered by the bed of the river. [Illustration: BIRD'S-EYE VIEW OF OLD FORT DEARBORN. _1. Main entrance of the fort passing beneath building, the upper story of which was directly over the passageway._ _2. Location of the "sally-part," or underground passage, running from the interior of the fort to the river._ _3. Gateway to the west._ _4. Blockhouse at the northwest corner of the fort._ _5. Blockhouse at the southeast corner of the fort._ _6. Officers' quarters._ _7. Barracks for the troops._ _8. Magazine._] It may be well to remark here that in the year 1833 a channel was dredged through the bar directly in line with the river's course. The old channel between the sand-bar and the shore gradually became filled up in the course of years, and at the present day it is which covered by a mass of earth, and forms a part of the area enclosed in Grant Park. In the construction of the fort there were two blockhouses erected, one at the southeast and the other at the northwest corner of the stockaded enclosure. These blockhouses projected partially beyond the line of pickets so that their defenders could command the approaches from the open spaces without the fort. On the north side of the fort there was a sally-port with a subterranean passage, leading from the parade ground within to the river bank, designed as a means of escape in case of emergency, or of obtaining a supply of water if needed, though a well was sunk for the ordinary uses of the garrison within the fort enclosure. Beyond the main line of pickets another similar line was placed at a different angle converging toward the blockhouses, thus providing two strong palisades entirely surrounding the fort. A plan for the construction of frontier forts was prepared by the War Department and this plan was referred to in a letter of instructions written by General Dearborn under date of June 28, 1804. While it thus appears that the letter was written a year later than the building of Fort Dearborn, it was an outline of the general principles by which the department had been governed in all such works. "Being of the opinion," wrote General Dearborn, "that for the general defense of our country we ought not to rely upon fortifications, but on men and steel, and that works calculated for resisting batteries of cannon are necessary only for our principal seaports, I cannot conceive it useful or expedient to construct expensive works for our interior military posts, especially such as are intended merely to hold the Indians in check."