  Massive disk galaxies like our Milky Way should host an ancient, metal-poor,
and centrally concentrated stellar population. This population reflects the
star formation and enrichment in the few most massive progenitor components
that coalesced at high redshift to form the proto-Galaxy. While metal-poor
stars are known to reside in the inner few kiloparsecs of our Galaxy, current
data do not yet provide a comprehensive picture of such a metal-poor "heart" of
the Milky Way. We use information from Gaia DR3, especially the XP spectra, to
construct a sample of 2 million bright (BP $<15.5$ mag) giant stars within
$30^\circ$ of the Galactic Center with robust [M/H] estimates, $\delta$ [M/H]
$\lesssim 0.1$. For most sample members we can calculate orbits based on Gaia
RVS velocities and astrometry. This sample reveals an extensive, ancient, and
metal-poor population that includes $\sim 18,000$ stars with $-2.7<$ [M/H]
$<-1.5$, representing a stellar mass of $\gtrsim 5\times 10^7$ M$_\odot$. The
spatial distribution of these [M/H] $<-1.5$ stars has a Gaussian extent of only
$\sigma_{\mathrm{R_{GC}}} \sim 2.7$ kpc around the Galactic center, with most
of these orbits being confined to the inner Galaxy. At high orbital
eccentricities, there is clear evidence for accreted halo stars in their
pericentral orbit phase. Stars with [M/H] $< -2$ show no net rotation, whereas
those with [M/H] $\sim -1$ are rotation dominated. Most of the tightly bound
stars show $[\alpha/\text{Fe}]$-enhancement and [Al/Fe]-[Mn/Fe] abundance
patterns expected for an origin in the more massive portions of the
proto-Galaxy. These central, metal-poor stars most likely predate the oldest
part of the disk ($\tau_{\text{age}}\approx 12.5$ Gyrs), which implies that
they formed at $z\gtrsim 5$, forging the proto-Milky Way.
