There are two possibilities for the traverse : direction W-E and the opposite, direction E-W.
The E-W-traverse described here takes advantage from the Schwarztor Bivy near the Schwarztor saddle, witch is an perfect place to start the traverse. The Schwarztor saddle is located between Breithorn and Pollux, from there the Bivy is visible.
The bivy (12 places, sometimes crowded) in most cases will be reached from the Klein Matterhorn cable car following the regular routes of Castor or Pollux crossing the Brethorn-Plateau (about 1.5 hours). Other possibilities are an ascent from Monte Rosa hut (a long, epic fight against crevasses) or from Italy from the Rif. Guide d'Ayas (1.5 hours).
The Breithorn traverse is crossing the summit of the 4000m-peaks of
- Rocia nera (east end of the Breithorn massive)
- Breithornzwillingen (east and west summit)
- Breithorn Mittelgipfel
- Breithorn Hauptgipfel
From the bivy you reach the saddle between Rocia Nera and Breithornzwillinge in about 1 hour on steep snow (easy but somewhat strenuous) wich starts directly behind the bivy. From the saddle go to the top of the Rocia Nera in a few minutes (cornices !).
Back at the saddle the route in general follows the crest of the main ridge. After an wide, easy snow ridge the climbing of the Breithornzwillinge gets somewhat steeper. Stay at the main ridge the whole time.
After those two summits the route goes down to an other snow saddle. Still following the ridge to the base of the most difficult part of the traverse : the ascent to the Breithorn Mittelgipfel. Here is a possible place to stop the traverse and escape direction S to the Breithornplateau and the path from Klein Matterhorn to Castor, Pollux and the bivy.
The ascent to the Breithorn Mittelgipfel needs rock climbing up to UIAA grade 4. Some steps, ledges and small gullys leading mostly at or near by the ridge to the summit of the Breithorn Mittelgipfel.
From there a easy snow ridgte leads to the main summit (W-summit) of the Breithorn.
Descent the regular route.
It will take about 8-9 hours from Schwarztor-Bivy to the main summit and one more hour from the summit to Kleines Matterhorn.
There are some big cornices at the whole ridge between Rocia Nera and main summit, so be very carefull.
Crampons, Helmet, Ice Axe, (Double-)Rope, Rocks, Nuts, Friends, Ice Screws, the complete things for combined stuff like this.
If you have information about this route that doesn't pertain to any of the other sections, please add it here.