Starting position #131
Back-rank setup: BNRQNKRB
SP-131 · BastionGuard — Off-centre king (c/f), no knight on the a- or h-file.
Move the pieces right on the board — full Chess960 rules, castle by dropping the king on the rook.
Position features
The king starts on f1, the rooks on c1 and g1, the queen on d1.
Castling short simply swaps the two pieces: the king on f1 and the rook on g1 trade places.
A bishop starts in the corner on a1: it has a single diagonal, which the b-pawn unlocks, running out to h8.
The second rank carries 2 pawns with no defender at all: a2, h2.
The setup belongs to the BastionGuard family; read right to left it becomes position 819.
The engine's main line opens with d4, putting a pawn straight into the centre.
Every sentence here is computed from the setup itself and can be checked on the board.
Balance
MBI 100 Morozov Balance Index: 100 of 100 — class A — most balanced.
- Engine evaluation of the starting position: 0 centipawns for White (depth 45, 400 000 000 nodes).
- Rank 7 of 960 by balance — 1 is the most balanced start.
- In 50 self-play games White scored 50.0% (95% CI 36.6–63.4%).
- Balance band E — even · dynamics along the play-out: equalizing
- Evaluation along the engine's main line (70 half-moves): +21 → +1 → +10 → 0
- Deeper check (4 000 000 000 nodes, depth 60): +5 cp, +5 cp against the base run — verified
- Sign verdict: even — within engine noise
- Self-play v2: 100 games at 1 000 000 nodes per move — White scored 50.5% (95% CI 40.9–60.1%)
Position facts
- Mirror twin: position #819
- The king starts on f, the rooks on c and g
- King and rook are neighbours — castling from adjacent squares feels unusual
- This position does not come up as the daily position in the next four years
Puzzles from this position
- Attack on the uncastled king: queen to d4 (d1·3) — Chess960 specifics · 780
- Attack on the uncastled king: bishop to b7 (g2) — Chess960 specifics · 780
- Winning blow: bishop to g7 (h8) — Chess960 specifics · 780
- Attack on the uncastled king: pawn to c6 (d5·29) — Chess960 specifics · 780
- Winning blow: queen to e6 (e5·2) — Chess960 specifics · 1060
- Attack on the uncastled king: bishop to a3 (b2·7) — Chess960 specifics · 1220
- Mate in 2: queen to g7 (g5) — Chess960 specifics · 1320
- Winning blow: queen to f6 (h8·7) — Chess960 specifics · 1510
- Mate in 3: pawn to d8 (d7) — Chess960 specifics · 1760
- Winning blow: pawn to e7 (e6·23) — Chess960 specifics · 2060
This position appears in course day 20
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Commentary
The engine reads this starting position as exactly level — one of the rare setups where it sees no edge at all on move one. Short castling swaps the king on f1 with the rook on g1. Both corners hold a bishop, a1 towards h8 and h1 towards a8, each with a single diagonal. The pawns on a2 and h2 begin with no defender at all, and f2 has only the king. The main line opens d4 d5, then g3 g6 b4 a5.
Written from the measured facts above and checked against the board before publishing. All 960 positions have one.