Complex sentence: At first, one race was held each year, on July 2; a second, on August 16, was added from 1701, though initially the August race was run intermittently rather than every year.
Split into simpler sentences: At first, one race was held each year, on July 2. A second, on August 16, was added from 1701, though initially the August race was run intermittently rather than every year.