  The MAGIC (Major Atmospheric Gamma-ray Imaging Cherenkov) telescopes observed
the BL Lac object H1722+119 (redshift unknown) for six consecutive nights
between 2013 May 17 and 22, for a total of 12.5 h. The observations were
triggered by high activity in the optical band measured by the KVA (Kungliga
Vetenskapsakademien) telescope. The source was for the first time detected in
the very high energy (VHE, $E > 100$ GeV) $\gamma$-ray band with a statistical
significance of 5.9 $\sigma$. The integral flux above 150 GeV is estimated to
be $(2.0\pm 0.5)$ per cent of the Crab Nebula flux. We used contemporaneous
high energy (HE, 100 MeV $ < E < 100$ GeV) $\gamma$-ray observations from
Fermi-LAT (Large Area Telescope) to estimate the redshift of the source. Within
the framework of the current extragalactic background light models, we estimate
the redshift to be $z = 0.34 \pm 0.15$. Additionally, we used contemporaneous
X-ray to radio data collected by the instruments on board the Swift satellite,
the KVA, and the OVRO (Owens Valley Radio Observatory) telescope to study
multifrequency characteristics of the source. We found no significant temporal
variability of the flux in the HE and VHE bands. The flux in the optical and
radio wavebands, on the other hand, did vary with different patterns. The
spectral energy distribution (SED) of H1722+119 shows surprising behaviour in
the $\sim 3\times10^{14} - 10^{18}$ Hz frequency range. It can be modelled
using an inhomogeneous helical jet synchrotron self-Compton model.
