Long diagonal

The board has two maximum-length diagonals. The dark-squared one runs from a1 to h8 through a1, b2, c3, d4, e5, f6, g7, and h8. The light-squared one runs from a8 to h1 through a8, b7, c6, d5, e4, f3, g2, and h1. Each contains eight squares , more than any other diagonal.

Both pass through the center and can connect one wing to the other. A bishop or queen can act over great distance along them, but only when no piece intervenes. A friendly piece stops the line; the first enemy piece may be captured, but it also prevents attacks beyond it.

The two eight-square diagonals

8

7

6

5

4

3

2

a1

b

c

d

e

f

g

h

The bishop reaches c3, but the friendly pawn on d4 stops the diagonal and blocks everything beyond it.

One clear line and one interrupted line

The bishop on b2 belongs to the dark-squared a1 to h8 diagonal, but the friendly pawn on d4 stops its reach after c3. The bishop on g2 belongs to the light-squared a8 to h1 diagonal and reaches e4 along a clear route. Both lines join opposite corners and cross two core central squares.

1. The bishop reaches c3, but the friendly pawn on d4 stops the diagonal and blocks everything beyond it.
2. The light-squared diagonal remains clear from g2 to a8 and passes through e4.

A fianchetto develops a bishop to b2, g2, b7, or g7 after the neighboring pawn has moved. This placement usually puts the bishop on a long diagonal and may give it influence over the center and the opposite wing, meaning the other side of the board. Merely standing there does not guarantee activity, because a pawn or piece in front of the bishop may still block it.