  We study the behavior of $r$-fold zeta-functions of Euler-Zagier type with
identical arguments $\zeta_r(s,s,\ldots,s)$ on the real line. Our basic tool is
an "infinite'' version of Newton's classical identities. We carry out numerical
computations, and draw graphs of $\zeta_r(s,s,\ldots,s)$ for real $s$, for
several small values of $r$. Those graphs suggest various properties of
$\zeta_r(s,s,\ldots,s)$, some of which we prove rigorously. When $s \in [0,1]$,
we show that $\zeta_r(s,s,\ldots,s)$ has $r$ asymptotes at $\Re s=1/k$ ($1\leq
k\leq r$), and determine the asymptotic behavior of $\zeta_r(s,s,\ldots,s)$
close to those asymptotes. Numerical computations establish the existence of
several real zeros for $2\leq r\leq 10$ (in which only the case $r=2$ was
previously known). Based on those computations, we raise a conjecture on the
number of zeros for general $r$, and gives a formula for calculating the number
of zeros. We also consider the behavior of $\zeta_r(s,s,\ldots,s)$ outside the
interval $[0,1]$. We prove asymptotic formulas for $\zeta_r(-k,-k,\ldots,-k)$,
where $k$ takes odd positive integer values and tends to $+\infty$. Moreover,
on the number of real zeros of $\zeta_r(s,s,\ldots,s)$, we prove that there are
exactly $(r-1)$ real zeros on the interrval $(-2n,-2(n-1))$ for any $n \geq 2$.
