In 1725 Christian Goldbach became professor of mathematics and historian at St Petersburg. Then, in 1728, he went to Moscow as tutor to Tsar Peter II. He travelled round Europe meeting mathematicians. He met Leibniz, Nicolaus(I) Bernoulli, Nicolaus(II) Bernoulli, de Moivre, Daniel Bernoulli and Hermann.
Goldbach did important work in number theory, much of it in correspondence with Euler. He is best remembered for his conjecture, made in 1742 in a letter to Euler and still an open question, that every even integer greater than 2 can be represented as the sum of two primes. Goldbach also conjectured that every odd number is the sum of three primes.
Vinogradov made progress on this second conjecture in 1937. Goldbach also studied infinite sums, the theory of curves and the theory of equations.