compassed around > encircled, surrounded
3 And lifted high above this earthly mass, 4 Which it surviewed, as hills do lower ground;
surviewed > overlooked, commanded
5 But not on ground might like to this be found,
on ground > in the world like to > [anything like]
6 Not that, which antique Cadmus whilom built
antique > ancient Cadmus > (Fl. c. 493 BC: the founder of Thebes) whilom > in ancient times
7 In Thebes, which Alexander did confound;
Thebes > (In Egypt, on both banks of the Nile, part of its site being later occupied by Luxor and Karnak) Alexander > (Alexander the Great, 356-323 BC, King of Macedon. Thebes was his first major conquest) confound > overthrow (see Met. 3.1-130)
8 Nor that proud tower of Troy, though richly gilt,