Step 1: Use the formula for time period of a simple pendulum.
For a simple pendulum,
\[
T=2\pi\sqrt{\frac{l}{g}}
\]
Given,
\[
T=4\,\text{s}
\]
and
\[
g=\pi^2\,\text{m/s}^2
\]
Step 2: Substitute the values.
\[
4=2\pi\sqrt{\frac{l}{\pi^2}}
\]
Divide both sides by \(2\pi\):
\[
\frac{2}{\pi}=\sqrt{\frac{l}{\pi^2}}
\]
Squaring both sides:
\[
\frac{4}{\pi^2}=\frac{l}{\pi^2}
\]
Multiplying by \(\pi^2\):
\[
l=4
\]
Step 3: Final conclusion.
Hence, the length of the pendulum is
\[
\boxed{4\,\text{m}}
\]