How many athletes competed in the first modern Olympics?

How to get close to this number

Reason from travel in 1896. Reaching Athens meant a long sea or rail journey paid for by the athlete or a private club, since national teams and funding did not yet exist. That barrier limits participation to a few hundred people from a handful of countries — the number is bounded by who could afford to go.

The comparison in the explanation is the whole point of the question: a few hundred athletes then against roughly ten thousand now, from fourteen nations against two hundred and six territories. A forty-fold increase in participants tracks the cost of travel falling and the idea of state-funded national teams being invented.

The two composition details are worth stating plainly: the first Games were all men, and the most recent reached gender parity for the first time. That is a hundred and twenty-eight years between an event that excluded half the species and one that did not, which is the more meaningful measure of change than the participant count.