Institutio Oratoria

For instance, while it is absurd to place a circumflex over all long syllables since the quantity of most syllables is obvious from the very nature of the word which is written, it is all the same occasionally necessary, since the same letter involves a different meaning according as it is long or short. For example we determine whether mains is to mean an

apple tree

or a

bad man

by the use of the circumflex;

palus means a

stake,

if the first syllable is long, a

marsh,

if it be short; again when the same letter is short in the nominative and long in the ablative, we generally require the circumflex to make it clear which quantity to understand.