CIRCLE - The Circle - The perfect shape of the circle expresses
wholeness and totality. It represents the principle which has no end
or beginning. It thus signifies the element of space.

CRESCENT MOON - This denotes the element of air. Air has the
capacity to expand. The female of the species shares this property with
air. This is exemplified in the expansion of a pregnant woman. Indeed
the crescent moon is an ancient symbol denoting femininity since the
waxing and waning of the moon is said to mirror a woman's menstrual
cycle.

CONICAL SPIRE - This signifies the element of fire. Fire, of
course, always rises upwards. When we kindle a fire it never burns
downwards but always goes straight up. So fire symbolizes energy
ascending upwards. It represents wisdom which burns away all
ignorance.

HEMISPHERICAL DOME - The main mass of the classical form of
the stupa consists of a solid,hemispherical dome. Early Buddhist texts
refer to this as the garbha, meaning 'womb' or 'container.' With this
reference the stupa as a whole is called the 'dhatu-garbha.' Dhatu is
Sanskrit for element. Herein lies the derivation of the word 'dagoba,'
which is the short form of dhatu-garbha and which is the most usual
designation of the stupa in Sri Lanka. Thus this section of a stupa is
an allusion to the primordial, creative waters. Indeed in all the major
cosmologies, life arose from the archetypal waters, a female symbol
of formless potentiality. The dome by virtue of representing the womb
from which issues all manifested existence signifies this creative matrix.

SQUARE BASE - This symbolizes the element earth. The phenomenal world spreads out in the four directions and the square with its four sides is an appropriate metaphor for the same. These four directions define the earth and bind it in order. Hence the square is the
perfect symbol to denote the terrestrial world. Often a stupa would have four gates, one for each direction, and various deities protecting the specific directions would stand guard over them.

Information from Exotic India website

     The symbolism of the form of the stupas is a vast and complex subject. The shape of the stupa represents the Buddha, crowned and sitting in meditation posture on a lion throne. The stupa also symbolizes the five elements and colors and their relationship to Enlightened Mind. Sections of the Stupa symbolize the Path of Enlightenment.

SPIRE - 13 Rings: the ten levels of the Mahayana path and the three highest stages of the Vajrayana path.

HARMIKA - Just below the spire: Eyes of the Buddha. The 8-fold Noble Path: Right View, Understanding, Speech, Action, Livelihood, Effort,
Mindfulness, Samadhi.

BUMPA - The Buddha’s chest: the 7 Elements of Enlightenment: Mindfulness, Discrimination, Exertion, Joy, Pliancy, Samadhi, Equanimity.

DOME - (4 Steps below Bumpa) - The legs of the Buddha: the 4 immeasurables of Loving Kindness, Compassion, Joy and Equanimity.

THRONE - (3 Steps at the Base) - The 3 refuges of Buddha, Dharma and Sangha.