might > could

5 And that bright tower, all built of crystal clean,

bright > bright; beautiful clean > {Clear, transparent; free from moral or spiritual pollution; pure and uncluttered in style}

6 Panthea, seemed the brightest thing that was:

Panthea > "All Sights", "Totality of Visions" (Greek, meaning
"Nonesuch", "Nonpareil", etc. Possibly identifiable as
Westminster Abbey or the Queen's Palace of Richmond)

7 But now by proof all otherwise I ween;

ween > think

8 For this great city that does far surpass, 9 And this bright angels' tower quite dims that tower of glass."

110.59

Most trew, then said the holy aged man;
2 Yet is Cleopolis for earthly +frame+,
The fairest peece, that eye beholden can:
4 And well beseemes all knights of noble name,
That couet in th'immortall booke of fame
6 To be eternized, that same to haunt,
And doen their seruice to that soueraigne Dame,
8 That glorie does to them for guerdon graunt:
For she is heauenly borne, and heauen may iustly vaunt.