  Arrangements of lines and pseudolines are fundamental objects in discrete and
computational geometry. They also appear in other areas of computer science,
such as the study of sorting networks. Let $B_n$ be the number of nonisomorphic
arrangements of $n$ pseudolines and let $b_n=\log_2{B_n}$. The problem of
estimating $B_n$ was posed by Knuth in 1992. Knuth conjectured that $b_n \leq
{n \choose 2} + o(n^2)$ and also derived the first upper and lower bounds: $b_n
\leq 0.7924 (n^2 +n)$ and $b_n \geq n^2/6 -O(n)$. The upper bound underwent
several improvements, $b_n \leq 0.6988\, n^2$ (Felsner, 1997), and $b_n \leq
0.6571\, n^2$ (Felsner and Valtr, 2011), for large $n$. Here we show that $b_n
\geq cn^2 -O(n \log{n})$ for some constant $c>0.2083$. In particular, $b_n \geq
0.2083\, n^2$ for large $n$. This improves the previous best lower bound, $b_n
\geq 0.1887\, n^2$, due to Felsner and Valtr (2011). Our arguments are
elementary and geometric in nature. Further, our constructions are likely to
spur new developments and improved lower bounds for related problems, such as
in topological graph drawings.
