  We show that there is a red-blue colouring of $[N]$ with no blue 3-term
arithmetic progression and no red arithmetic progression of length $e^{C(\log
N)^{3/4}(\log \log N)^{1/4}}$. Consequently, the two-colour van der Waerden
number $w(3,k)$ is bounded below by $k^{b(k)}$, where $b(k) = c \big(
\frac{\log k}{\log\log k} \big)^{1/3}$. Previously it had been speculated,
supported by data, that $w(3,k) = O(k^2)$.
