Train from Barcelona to Montpellier &#40;buy tickets online?&#41;
<p>I&#39;ve found one route I&#39;d like to take to get from Barcelona to Montpellier on the DB Bahn site. It&#39;s on a Sunday &#40;April 28&#41;, so the options are more limited.</p> <p>Barcelona Sants to Cerbere &#40;Regionalzug&#41; <br />Cerbere to Narbonne &#40;Regional-Express&#41; <br />
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I've found one route I'd like to take to get from Barcelona to Montpellier on the DB Bahn site. It's on a Sunday (April 28), so the options are more limited. Barcelona Sants to Cerbere (Regionalzug) Cerbere to Narbonne (Regional-Express)

Narbonna to Montpellier Saint-Roch (Regional-Express) This route does not appear at all on the RailEurope site. I've never traveled in Europe and I'm completely confused about the trains. Is it because these are regional trains? Are these available online anywhere for purchase? Should we worry about this route being booked? We will be doing a limited amount of train travel (we will be renting a car for a few days) so we will not be purchasing a pass. Also when a train says compulsory reservation, does that mean it must be booked ahead of time (weeks in advance) or can it be done at the time of travel? I'm seeing compulsory reservations for a trip from Nice to La Spezia. Any advice would be much appreciated!