  This paper analyzes the performance of multiple reconfigurable intelligent
surfaces (RISs)-aided networks. The paper also provides some optimization
results on the number of reflecting elements on RISs and the optimal placement
of RISs. We first derive accurate closed-form approximations for RIS channels'
distributions assuming independent non-identically distributed (i.ni.d.)
Nakagami-\emph{m} fading environment. Then, the approximate expressions for
outage probability (OP) and average symbol error probability are derived in
closed-form. Furthermore, to get more insights into the system performance, we
derive the asymptotic OP at the high signal-to-noise ratio regime and provide
closed-form expressions for the system diversity order and coding gain.
Finally, the accuracy of our theoretical analysis is validated through
Monte-Carlo simulations. The obtained results show that the considered RIS
scenario can provide a diversity order of $\frac{a}{2}K$, where $a$ is a
function of the Nakagami fading parameter $m$ and the number of meta-surface
elements $N$, and $K$ is the number of RISs.
