  We analyze eight epochs of Hubble Space Telescope H$\alpha$+[N II] imaging of
Eta Carinae's outer ejecta. Proper motions of nearly 800 knots reveal that the
detected ejecta are divided into three apparent age groups, dating to around
1250 A.D., to around 1550 A.D., and to during or shortly before the Great
Eruption of the 1840s. Ejecta from these groups reside in different locations
and provide a firm constraint that Eta Car experienced multiple major eruptions
prior to the 19th century. The 1250 and 1550 events did not share the same
axisymmetry as the Homunculus; the 1250 event was particularly asymmetric, even
one-sided. In addition, the ejecta in the S ridge, which have been associated
with the Great Eruption, appear to predate the ejection of the Homunculus by
several decades. We detect essentially ballistic expansion across multiple
epochs. We find no evidence for large-scale deceleration of the observed knots
that could power the soft X-ray shell by plowing into surrounding material,
suggesting that the observed X-rays arise instead from fast, rarefied ejecta
from the 1840s overtaking the older dense knots. Early deceleration and
subsequent coasting cannot explain the origin of the older outer
ejecta---significant episodic mass loss prior to the 19th century is required.
The timescale and geometry of the past eruptions provide important constraints
for any theoretical physical mechanisms driving Eta Car's behavior.
Non-repeating mechanisms such as the merger of a close binary in a triple
system would require additional complexities to explain the observations.
