This figure is composed of 4 planets, all in square aspect (90°) to each other, forming a box. The planets of opposing corners of the box are in opposition (180°) to each other.
The energy of the Grand Cross is typically intense, stressful, motivating and dynamic. Its energy can be used to work hard in some area, and can indicate a tendency to get stuck in "perpetual motion."
This figure can be separated into four T-square patterns. Whereas the T-square has one apex planet, the Grand Cross has no particular apex planet—or you might say it has nothing but apex planets! The apex planet in an aspect figure is a focal point that steers or directs the figure's energy. When all of the planets are an apex planet, you can see how the Grand Cross tends to have very dynamic, perpetual energy.
As with the T-square, the Grand Cross ideally involves planets in signs of the same modality: Cardinal, Fixed or Mutable.
In Cardinal signs (Aries, Cancer, Libra, Capricorn), the person is usually very goal-driven and creative. They may love to start new projects, but lose interest when it comes to follow through to the end. They may have multiple projects and activities going at once, as they discover new ideas and possibilities to pursue.
In Fixed signs (Taurus, Leo, Scorpio, Aquarius), the person may find it extremely hard to get started with new projects, but they have staying power to maintain a constant effort. With all that Fixed energy, it's hard to let go once they're in holding-on mode, and hard to stop when they need rest.
In Mutable signs (Gemini, Virgo, Sagittarius, Pisces), the person is often very adaptable and flexible...to the point of sometimes being unpredictable, unreliable or lacking a solid identity. They may be easily influenced or distracted by new information, which is an asset in a constantly changing situation but not so much in a situation that requires consistency.
In Huber astrology, this is called an Achievement Square.