Taurus, Leo, Scorpio, Aquarius. The middle of each season, when it is established and going nowhere.
Fixed signs occupy the second month of each season, the stretch where the weather has settled and nothing is turning. Taurus in mid-spring, Leo in high summer, Scorpio in mid-autumn, Aquarius in deep winter.
They form their own cross, 90° apart and offset 30° from the cardinal one. The four fixed signs are the traditional symbols of the evangelists — bull, lion, eagle (for Scorpio) and man (for Aquarius) — which is why those four figures appear together in so much medieval art.
A chart weighted toward fixed signs will tend to show squares and oppositions between those placements rather than trines, for the same reason a fire-weighted chart shows trines: the geometry is doing the work.