Via Combusta
The Via Combusta, the burned path, is the belt from about 15 degrees of Libra to about 15 degrees of Scorpio, which classical astrology marks as unfavourable ground for the Moon.
Two reasons are given. Both lights are debilitated across it, the Sun in its fall in Libra and the Moon in its fall in Scorpio, and the stretch carries an unusual number of the fixed stars the tradition read as violent. The second half of that argument has aged least well, because precession has moved those stars on while the degrees stayed put.
The standard exception is 23 degrees of Libra, where Spica sits, which is held to be fortunate enough to cancel the caution. It belongs to horary and electional judgement rather than to natal reading: a natal Moon in the belt is common and carries no verdict.
Frequently asked
Which degrees does the Via Combusta cover?
Most commonly 15 degrees of Libra to 15 degrees of Scorpio, though some authors begin it at 0 Libra and a few extend it through all of Scorpio.
Does it matter in a birth chart?
Very little. It questions whether a horary chart is fit to judge or a moment fit to begin in, and a natal Moon there is not read as a verdict.