The perimeter ring in Piazza del Campo, normally paved in "pietra serena", is coverd by a layer of earth composed of a mix of "tufo" and sand. The thickness of this layer, although varying at different points, results in an average thickness of about 15 cm. The desired compactness is obtained by the use of steam rollers. By watering it periodically, the earth is not allowed to become too dry, and as a result it is maintained elastic and compact. Overall, however, it is a "hard" earth in respect to normal race track conditions.

In the past, this is how the dirt for the race-course was spread on the pavement of the Piazza

The length of the circuit, if measured along a straight line, is 339 meters in length and seeing as how the race is run 3 times around the Piazza, horses complete a theoretical course of 1070 meters. Based on the times and statistics conducted on this terrain regarding the Palios since WWII, the "fast" races have a total time of 1'15" - 1'16", while the "slow" races have a total time above 1'20". The present track record is the Palio race that was run on August 16, 1987 (horse Benito, jockey, Cianchino, time: 1'14", won by the Panther contrada). The external and internal borders of the course are diminished by appropriate barricades that in certain points actually reduce the natural width of the track to make room for the bleachers. Protective padding is placed in appropriate places.

The planimetry (analysed in detail in the following design refers to the course without the earth down on the pavement) has been described in 4 distinct zones, each one of which offers different characteristics.

Planimetry of the Piazza del Campo in Siena

The "A" section is similiar to the shape of a portion of a circle; it is flat in its length with a slight slope towards the interior.

The "B" section includes the curve at San Martino that, with its internal borders, form a 95° angle. The first part of this zone has a slight descent and it is transversally inclined with a 90 cm difference in the gradient level between the two borders. The second part has a sharp descent (8%), and in the transvers section there is a difference of at least a meter in the gradient level.

The "C" area corresponds to a section in a straight line where the descent of the previous section "B" ends and the upward incline of the "Casato" section begins, seperated by a flat stretch.

The "D" section includes the 92° curve at "Casato". Before this there is an incline which is accentuated in the last 15 meters consisting of a 10.5% slope. The upper stretch continues slightly uphill, then levels out before joining the "A" stretch.

On the basis of a detailed reconstruction of horse accidents which have happened on this race-track during the last 20 years of the Palio, we see that the greatest number of accidents have happened at San Martino (57% of the cases) in respect to "Casato" (37% of the cases.)

But while at the curve at San Martino the accidents have happened both on the first lap (45%) as well as on the second lap (55%), at the "Casato" curve the accidents have happened mostly on the first lap (70%).

We can therefore deduce that:

1) the risk is greater at the curve at San Martino;
2) the curve at "Casato" is risker than the others in relationship to the crowding factor, normal during the first time around, while the risk at San Martino, besides the crowding factor is also risky due to the sloping factor.
Therefore, this risk factor, particular to the curve at San Martino, is present both during the first and the second time around, which are the fastest circuits.