  Six low-luminosity active galactic nuclei have been imaged at multiple
frequencies from 1.7--43 GHz (2.3--15 GHz for three of the galaxies) using the
Very Long Baseline Array. In spite of dynamic ranges of about 100 in several
frequency bands, all six galaxies remain unresolved, with size limits at 8.4
GHz of 10^3--10^4 times the Schwarzschild radii of the black holes inferred at
their galactic centers. The galaxy spectra are roughly flat from 1.7 to 43 GHz,
rather than steepening to classical optically thin synchrotron spectra at high
frequencies. Although the spectral slopes somewhat resemble predictions for
advection-dominated accretion flows, the luminosities are too high for the
black hole masses of the galaxies and the slight spectral steepening at high
frequencies cannot be explained by standard simple models of such accretion
flows. In contrast, compact jets can accommodate the average spectral index,
the relatively high radio luminosity, and the unresolved appearance, but only
if the jets in all six galaxies are fairly close to our line of sight. This
constraint is in agreement with inclination angle predictions for five of the
six AGNs based on the dusty torus unification model.
