different between thereas vs whereto

Middle English

thereas

where; in the place where.
- Than Sir Bors departed secretly uppon a day and rode unto Sir Launcelot thereas he was with the ermyte Sir Brascias, and tolde hym of all thys adventure.

From Middle English wherto, equivalent to where +? to.

whereto (not comparable)

(archaic, interrogative) To what; to which place, whither?
(obsolete, interrogative) To what end; wherefore?
(archaic, relative) To which.
- 1658, Thomas Browne, The Garden of Cyrus:
  According whereto Xenophon describeth his gallant plantation at Sardis, thus rendred by Strebæus.

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