The Bill of Rights ensures people's rights are protected if they are being arrested through:
People must be told what they are being charged with.
This concept is also known as “Miranda Rights” (Fifth Amemdmemt).
There are of course more than three purposes of a democratic constitution, but perhaps the three most important are to declare popular sovereignty, the rule of law, and the separation of powers.
There were a lot of factors, but it mainly was caused by the breakdown of leadership in the Roman Empire. After Julius Caesar was assassinated, the conspirators were unable to regain leadership and eventually all died or killed themselves during the civil war, in which Octavius or Augustus Caesar (Caesar's adopted son) and Mark Antony took back leadership. Eventually, their rule fell apart and other outside forces tried and succeeded in undermining the trust the Roman citizens had in the Roman government, and those outside forces easily defeated Rome, causing it to fall apart forever.
The answer is: Scientists study how things work while engineers create new things
