For goodness sakes folks, your on the internet, why speculate, a search reveals :
"The length of a marathon was not fixed at first, since the only important factor was that all athletes competed on the same course. The marathon races in the first few Olympic Games were not of a set length, but were approximately 40 km,[10] roughly the distance from Marathon to Athens by the longer, flatter route. The exact length of the Olympic marathon varied depending on the route established for each venue.
The marathon at the 1908 Summer Olympics in London was set to measure about 25 miles (40 km) and to start on ‘The Long Walk’ – a magnificent avenue leading up to Windsor Castle in the grounds of Windsor Great Park. The Princess of Wales wanted her children to watch the start of the race, so the start of the race was moved to the east lawn of Windsor Castle, increasing its length to 26 miles (42 km).[10] The race was to finish at the Great White City Stadium in Shepherd's Bush in London; however, Queen Alexandra insisted on having the best view of the finish; so, in the words of the official Olympic report, "385 yards were run on the cinder track to the finish, below the Royal Box".[10] The length then became 42.195 km (26 miles 385 yards or 26 7⁄32 miles).
For the next Olympics in 1912, the length was changed to 40.2 km (24.98 miles) and changed again to 42.75 km (26.56 miles) for the 1920 Olympics until it was fixed at the 1908 distance for the 1924 Olympics. In fact, of the first seven Olympic Games, there were six different marathon distances between 40 km and 42.75 km (40 km being used twice).
Following the 1908 Olympics in London, an annual event called the Polytechnic Marathon had been instituted over the 1908 distance of 26 miles 385 yards (42.195 km), and it was largely due to the prestige of the Polytechnic Marathon that 42.195 km was adopted as the official marathon distance in 1921 by the International Amateur Athletic Federation (IAAF) - Rule 240 of their Competition Rules.[1]. The difference between 42.195 km and 26 miles 385 yards is 1.2 centimetres. The difference between the standard distance and the rounded figure frequently employed (as in the table), 26.22 miles, is a little over two metres."
