  The cross section of the $t\bar{t}Z$~and $t\bar{t}W$~processes are measured
in a simultaneous fit using 36.1 $\text{fb}^{-1}$ of of proton--proton
collisions at a centre-of-mass energy of $\sqrt{s}=13$ TeV recorded by the
ATLAS experiment at the LHC. In addition, a fit is performed in the 4$\ell$
channel only, resulting in a cross section of $\sigma_{t\bar{t}Z} = 1.07 \pm
0.26 \,\text{pb}$. This result is consistent with the combined fit and agrees
with the prediction by the Standard Model.
