His work changed the understanding and knowledge of mathematics in the Middle Ages and mathematicians in Europe read his book. They began to use these Hindu–Arabic numerals (0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, ...) instead of the Roman numerals (I, II, III, IV, V, VI, VII, VIII, IX, X, ...). The Arabic numeral system is easier to do mathematics with, as Roman numbers have no place values. This means that they can only deal with whole numbers and do simple equations. Roman numerals also have no number zero.