Mares or Mareis: How To spell?

The word Mares is misspelled against Mareis, a noun meaning "A Marsh."

Word contains consecutive vowels 'EI' in between alphabets mar & s is misspelled as 'E' as letter 'I' is phonetically ignored
Wrong Spelling:  mar-e-s 
Correct Spelling:  mar-ei-s 
Explore spell check of Mareis to spell without errors.