At a glance:

The Brahmasthana (the central square of the plot) is an important factor to be reckoned while constructing a building. The Brahmasthana is the region round the navel (Nabhi) of the Vastu Purusha (site deity). The energy lines running through the centre of the plot are also equally important

In ancient times villages, towns, temples (Prasada), palaces (Rajagriha) and even dwelling places (Sala) were constructed in such a manner that the central portions either contained a temple, deity, courtyard or (in the case of a village or town) a huge central hall for the assembly of people.

The central portion called the Brahmasthana corresponds to the nine squares of the 81 grid plan (also called the paramasayika padavinyasa). The Brahmasthana is the region round the navel (Nabhi) of the Vastu Purusha (site deity).

Brihat Samhita says:
Sukhamicchan brahmanaam
yatnadhragrihanthaha stham I
Uchishtadhyupathadgrihapathiroopathapyathe
thasmin II

A house-owner (Yajamana) who wants happiness should safeguard very carefully Brahman (the central nine squares). Affliction in this area by way of unclean things like leftovers would harm the owner of the site.

The Manasara unequivocally states that in the Brahmasthana, the temple of the family deity can be built.
The wise men of ancient India also talked about certain lines running across a site crossing the Brahmasthana. As these lines corresponded to several body parts of the Vastu Purusha, they concluded that much care was to be taken in building a structure, so that these parts were not ‘hurt’. The points at which these lines cut the Brahmasthana were also to be guarded carefully.

In fact, Mayamata also talks about vulnerable points and calls them Marma. These are the lines joining the north with south and the east with west. The north-south line is called Nadi and the east-west line Vamsa. The diagonals running across the Brahmasthana are called Konasutra. These are highly sensitive energy lines.

The Brihat Samhita also talks about these vulnerable points. It states that the meeting points of the longer diagonals and the exact middle points of the squares have to be considered as vulnerable points which ought not to be hurt.

Brihat Samhita (Ch.LIII, Stanza 58) says that if these vulnerable points are ‘hurt’ by nails, pillars, pegs, heavy objects etc., the owner will be troubled in the corresponding limbs of his body.

It becomes clear that the Brahmasthana and the energy lines have to be safeguarded.