We hadn't booked initially, thinking that even though it was Easter Sunday, it might not be necessary so early in the year. However, the queues were already quite long. So we went off for lunch and booked using a mobile, then we were able to walk straight in, bypassing the queue and simply showing our e-tickets on my mobile. Couldn't have been simpler, and saved such a lot of time and hassle. And the castle and ramparts are well worth visiting.
The restored 12th-century hilltop castle, the Chateau Comtal, is at the heart of the ancient City of Carcassonne and is a massive, sprawling edifice of significant historical importance. As we were visiting it late in the season we probably did not need to worry about 'skipping the line' as there were not so many visitors but in the summer months it would doubtless be advisable. We thoroughly enjoyed exploring the World Heritage Gallo-Roman and medieval military architecture. The ramparts were not open on the day of our visit but we were allowed back the following day to walk the three kilometres of ramparts and towers which offer fantastic views of the surrounding area. We would thoroughly recommend.