At a distance of 3.4 Mpc , NGC 5128 ( Centaurus A ) is by far the nearest active radio galaxy .
It is often considered to be the prototype Fanaroff-Riley Class I ‘ low-luminosity ’ radio galaxy , and as such it plays an important role in our understanding of a major class of active galaxies .
Its proximity has spawned numerous detailed investigations of its properties , yielding unrivalled but still incomplete knowledge of its structure and dynamics .

The massive elliptical host galaxy is moderately triaxial and contains a thin , strongly warped disk rich in dust , atomic and molecular gas and luminous young stars .
Its globular cluster ensemble has a bimodal distribution of metallicities .
Deep optical images reveal faint major axis extensions as well as a system of filaments and shells .
These and other characteristics are generally regarded as strong evidence that NGC 5128 has experienced a major merging events at least once in its past .

The galaxy has a very compact , subparsec nucleus exhibiting noticeable intensity variations at radio and X-ray wavelengths , probably powered by accretion events .
The central object may be a black hole of moderate mass .
Towards the nucleus , rich absorption spectra of atomic hydrogen and various molecular species suggest the presence of significant amounts of material falling into the nucleus , presumably ‘ feeding the monster ’ .
Emanating from the nucleus are linear radio/X-ray jets , becoming subrelativistic at a few parsec from the nucleus .
At about 5 kpc from the nucleus , the jets expand into plumes .
Huge radio lobes extend beyond the plumes out to to 250 kpc .
A compact circumnuclear disk with a central cavity surrounds the nucleus .
Its plane , although at an angle to the minor axis of the galaxy , is perpendicular to the inner jets .
The jet-collimating mechanism , probably connected to the circumnuclear disk , appears to precess on timescales of order a few times 10 ^ { 7 } years .

This review summarizes the present state of knowledge of NGC 5128 and its associated radio source Centaurus A .
Underlying physical processes are outside its scope : they are briefly referred to , but not discussed .

\keywords Galaxies : active ( 11.01.2 ) – Galaxies : individual : NGC 5128 ( 11.09.1 ) – Galaxies : jets ( 11.10.1 ) – Infrared : galaxies ( 13.09.1 ) – Radio continuum : galaxies ( 13.18.1 ) – X-rays : galaxies ( 13.25.2 )