In the poem, "The Star-Spangled banner," the synonym for fortified elevation is ramparts. Look at the usage of the word in the lines given below, "O'er the ramparts we watched," it is evident that a reference is being made to something that is elevated and acts as a barrier to protect the viewers from the flying rockets and bombs.
Whose broad stripes and bright stars through the perilous fight,
O'er the ramparts we watched were so gallantly streaming;
And the rocket's red glare, the bombs bursting in air,
The definition for a rampart as given at http://dictionary.reference.com is "a broad elevation or mound of earth raised as a fortification around a place and usually capped with a stone or earth parapet." The other terms: reposes, host, ocean and banner do not mean a fortified elevation.