The massive Romanesque wall is thick for a reason, which has to do with its function.
The walls support whole weight of the vaulting roof,
with slight reinforcement of pillars set along the wall, but no external
system of buttressing to resist the lateral thrust of the upper arches.
Lateral thrust is the force that moves vertically at the top of an arch or
horizontally a the place where the vault meets the vertical walls.
We observe the lack of external buttressing in this image of
the Abbey Church of Saint-Benoit sur Loire or
the church of Saint-Savin-sur-Gartempe in Vienne.
In Romanesque churches, the problem of lateral thrust is dealt with
from the inside, as we see in this cross-section of the church of Conques.
What we see from the outside is a series of radiating chapels in the eastern part,
or cheve, which will become the choir of Gothic cathedrals.
There are no external buttresses in Romanesque churches
to carry the weight of high walls to the ground.
The church reaches the height that it does through an internal system of vaults
posed on top of each other, as in the outside of Conques.