Who are Sabeans?

In [Surat Al-Baqarah ayah 62](http://quran.com/2/62) , Allah (The Glorified) says; > Sahih International
Indeed, those who believed and those who were Jews > or Christians or Sabeans [before Prophet Muhammad] - those [among > them] who believed in Allah and the Last Day and did righteousness - > will have their reward with their Lord, and no fear will there be > concerning them, nor will they grieve. Who were (or are?) the people called الصابئين according to this ayah, and what makes them relevant in the context of this ayah? How are they similar with Jews or Christians? I assume similarity because they were mentioned alongside Jews and Christians.