So if it starts in Portugal, how do they drive across the Straits of Gilbraltar?
Ferry. The race is broken up into liason (non-timed portages, if you will) and timed specials. They are only on the road 8-18 hours a day. It's not as if they drop a green flag in Lisbon and the first one to Dakar wins. ts much more heavily organized.
All cars must be road-legal and registered for travel on all the roads in each country they visit.