Three ages > (Nestor had already counselled two generations of Greeks before he came to advise Agamemnon (Iliad 1.247-52)) contrive > wear down (of time); hence: live through

6 By whose advice old Priam's city fell),

By > [And by]
Priam > (The last king of Troy)

7 With these in praise of policies might strive.

praise > praiseworthiness

8 These three in these three rooms did sundry dwell,

sundry > separately

9 And counselled fair Alma how to govern well.

209.49

The first of them could things to come foresee:
2 The next could of things present best aduize;
The third things past could keepe in memoree,
4 So that no time, nor +reason+ could arize,
But that the same could one of these comprize.
6 For thy the first did in the forepart sit,
That nought mote hinder his quicke preiudize:
8 He had a sharpe foresight, and working wit,
That neuer idle was, ne once +could+ rest a whit.