How does the poet immortalize his beloved in the poem, "Not Marble, nor Guilded Monuments" ?

The Poet imortalizes his friend by writting a poem and explaining it as the most durable thing ever

.He also compare various things like the work of masonary ,sword of the great god of war ,vast architectral monuments destroyed by the the slutish time but the poem will not perish till the time the memories of his friend is in the mind of his friend

Also he says that generations after generations will come and remember his friend (likewise we at present remembering him ) tillthe day the wold is not destroyed