In 1805 and early 1806, the President began to appoint leaders for the expedition. For the scientists, he chose the astronomer/surveyor Thomas Freeman, (who had recently been with Andrew Ellicott on his survey of the southern boundary of the United States) and Peter Custis (the first academically trained naturalist to accompany an expedition, he was still a medical student in Philadelphia. He served as the group's botanist and ethnographer). Captain Richard Sparks was chosen to lead the military troops. As the departure date of the expedition grew closer, more soldiers were recruited until the group numbered twenty-four in all.