  The broad-line region (BLR) of active galactic nuclei (AGNs) traces gas close
to the central supermassive black hole (BH). Recent reverberation mapping (RM)
and interferometric spectro-astrometry data have enabled detailed
investigations of the BLR structure and dynamics, as well as estimates of the
BH mass. These exciting developments motivate comparative investigations of BLR
structures using different broad emission lines. In this work, we have
developed a method to simultaneously model multiple broad lines of the BLR from
a single-epoch spectrum. We apply this method to the five strongest broad
emission lines (H$\alpha$, H$\beta$, H$\gamma$, Pa$\beta$, and He
$I\;\lambda$5876) in the UV-to-NIR spectrum of NGC 3783, a nearby Type I AGN
which has been well studied by RM and interferometric observations. Fixing the
BH mass to the published value, we fit these line profiles simultaneously to
constrain the BLR structure. We find that the differences between line profiles
can be explained almost entirely as being due to different radial distributions
of the line emission. We find that using multiple lines in this way also
enables one to measure some important physical parameters, such as the
inclination angle and virial factor of the BLR. The ratios of the derived BLR
time lags are consistent with the expectation of theoretical model calculations
and RM measurements.
