In order to stimulate interest in geometry, model the use of complex, real-world applications of mathematics for prospective teachers, and draw a connection between mathematics, history, and culture, a lesson was designed in which students replicate the experiment of Eratosthenes of Cyrene (c. 275–194 B.C.) to estimate the circumference of the earth. During the lesson, students measure the angle of inclination of the sun on a date near the spring equinox and build models of the situation using dynamic geometry software. This process helps prospective teachers develop knowledge about modeling situations, measurement, similar figures, and other geometric topics.