  We carry out a dedicated study of 3XMM J181923.7$-$170616\ with an
approximate pulsation period of 400~s using the XMM-Newton and Swift
observations spanning across nine years. We have refined the period of the
source to 407.904(7) s (at epoch MJD 57142) and determined a period derivative
limit of $\dot{P}{\leq} 5.9\pm 5.4\times 10^{-9} s s^{-1}$ ($1\sigma$). The
source radiates hard, persistent X-ray emission during the observation epochs,
which is best described by an absorbed \powerlaw\ model ($\Gamma \sim
0.2$--0.8) plus faint Fe lines at 6.4 keV and 6.7 keV. The X-ray flux revealed
a variation within a factor of 2, along with a spectral hardening as the flux
increased. The pulse shape is sinusoid-like and the spectral properties of
different phases do not present significant variation. The absorption N$_H$
$\sim 1.3\times 10^{22} cm^{-2}$ is similar to the total Galactic hydrogen
column density along the direction, indicating that it is a distant source. A
search for the counterpart in optical and near-infrared surveys reveals a low
mass K-type giant, while the existence of a Galactic OB supergiant is excluded.
A symbiotic X-ray binary is the favored nature of 3XMM J181923.7$-$170616 and
can essentially explain the low luminosity of ${2.78\times 10^{34} d_{10}^{2}
erg s^{-1}}$, slow pulsation, hard X-ray spectrum, and possible K3~III
companion. An alternative explanation of the source is a persistent Be/X-ray
binary with a companion star no earlier than B3-type.
