Defense of Savannah.Savannah was better protected by nature from attack by land or water than any other city near the Atlantic seaboard. Stretching to the north, east, and southward lay swamps and morasses through which ran the river-approach of twelve miles to the town. Innumerable small creeks separated the marshes into islands over which it was out of the question for an army to march without first building roads and bridging miles of waterways. The Federal fleet had for months been on the blockade off the mouth of the river, and Savannah had been closed to blockade runners since the fall of Fort Pulaski in April, 1862. But obstructions and powerful batteries held the river, and Fort McAllister, ten miles to the south, on the Ogeechee, still held the city safe in its guardianship.