In the beginning there was a racecourse (yes, honestly), and a special train station was built for it, called Gatwick Racecourse.
Then it got turned in the 1930s into an airfield. Grass of course. The Beehive building got built close to the train station, which got a new name. But the ground was not drained enough, and the operators that moved in there in the mid-1930s (like the original British Airways) moved on elsewhere after losing too much winter ops to waterlogging.
In the 1950s there was another go, same overall airfield but with the facilities built on the northern side. New train station was built north of the old one (this latter was on the site of today's train sidings where trains wait between trips, about 1/2 mile south of the current station, still known to railway staff as the "Racecourse Sidings"). New terminal building (now buried in the middle of the South terminal) linked to the station by a footbridge. New runway, hard of course, which forms the east end of the present main runway. Proper drains doubtless put in. All very much extended since it reopened.
"Both" runways were built at the same time, because one is an actual runway from the 1958 rebuild and the other is an emergency use of the taxiway opened at the same time. Renumbered to two runways following a couple of misunderstanding close-calls in the 1980s when the adapted taxiway was in use, its transition from taxiway was gradual, in stages.
The Beehive was left out on a limb after all this.