What were some weaknesses and strengths of the Roman Empire?

This question
likely refers to the whole history of Rome from 8th B.C.E to the 5th century C.E. despite the
reference to the Empire that existed from the time of Augustus to the Barbarian invasions in the
West and even longer in the eastern Roman (Byzantine) Empire. To this end, it is better to have
more information, especially as each phase of Roman civilization (monarchy, republic, monarchy)
transitioned from from the last, creating very gradual changes.

Some
strengths of Rome were its military power. Not only was Rome's professional army unique at its
height, their tactics and commanders were second to none. The various legions of the Roman army
were loyal to Rome and not their commanders, so the fight for their civilization and way of life
gave them a tenacious fighting determination. Close range weapons (gladius) worked in tandem
with the shields and spears designed for long range disruption of enemy formation. Romans also
learned from their enemies, be it the development of ships in the First Punic War or how to
counter the threat of Hannibal's war elephants in the Second at Zama.

Romans
were also skilled administrators, building the roads and communication tools that were necessary
if they were to have large areas of land under the control of one people. Even though Rome
largely expanded due to the threat of enemies all around their borders (which naturally
persisted as the Empire expanded and during periods of shoddy Emperors), their systems were
effective to the point that it would take more than a powerful enemy to bring them down. It is
almost a boring answer, but Rome more destroyed itself through internal problems than it was
outright conquered. Their enemies merely noticed and took advantage, as a system can only
persist if the people are dedicated to it. Apathy is the real weakness in the fall of many an
empire.

Other weaknesses included power too concentrated in the Senate and
later the Emperor. While consolidation of power works with benevolent leaders who serve the
public rather than their own ambition (Cincinnatus) it was rarely the case with the patrician
class, what with the wealthy Roman senators serving their political ambitions rather than the
good of Rome, the ability for few to climb the cursus honorum, and the flagrant violations of
the rules designed to hold ambition in check (ie: no repeated holdings of offices; longer term
limits) in the final generation of the Roman Republic. During the specific Empire period, there
was also the choosing of Emperors by the Praetorian Guard, which caused short and often chaotic
reigns, as these guards' favoritism would wax and wane, especially as they were the military
presence within the city of Rome during this time. This made administration difficult and
brought the notice of the enemies of Rome.