What language did Helen begin learning with Mr. Irons?

From the text:

Mr. Irons, a neighbour of theirs, was a good Latin scholar; it was arranged that I should study under him. I remember him as a man of rare, sweet nature and of wide experience. He taught me Latin grammar principally; but he often helped me in arithmetic, which I found as troublesome as it was uninteresting. Mr. Irons also read with me Tennyson's "In Memoriam."