Today, the Congress Commemorative Half Dollar Coin remembers when 300-400 armed soldiers surrounded the congressional meeting in the State House 234 years ago.
From The Papers of James Madison, Volume I, published in 1842:
Saturday, June 21st. 
The mutinous soldiers presented themselves, drawn up in the street before the State House, where Congress had assembled.
The Executive Council of the State, sitting under the same roof, was called on for the proper interposition.
President Dickinson came in, and explained the difficulty, under actual circumstances, of bringing out the militia of the place for the suppression of the mutiny. He thought that without some outrages on persons or property, the militia could not be relied on.
General St. Clair, then in Philadelphia, was sent for, and desired to use his interposition, in order to prevail on the troops to return to the barracks.
His report gave no encouragement.
In this posture of things, it was proposed by Mr. Izard, that Congress should adjourn.
It was proposed by Mr. Hamilton, that General St. Clair, in concert with the Executive Council of the State, should take order for terminating the mutiny.
Mr. Reed moved, that the General should endeavor to withdraw the troops, by assuring them of the disposition of Congress to do them justice.
It was finally agreed, that Congress should remain till the usual hour of adjournment, but without taking any step in relation to the alleged grievances of the soldiers, or any other business whatever.
In the mean time, the soldiers remained in their position, without offering any violence, — individuals only, occasionally, uttering offensive words, and wantonly pointing their muskets to the windows of the Hall of Congress.
No danger from premeditated violence was apprehended, but it was observed that spirituous drink, from the tippling-houses adjoining, began to be liberally served out to the soldiers, and might lead to hasty excesses.
None were committed, however, and about three o’clock, the usual hour, Congress adjourned; the soldiers, though in some instances offering a mock obstruction, permitting the members to pass through their ranks.
They soon afterwards retired themselves to the barracks.
In the evening Congress reassembled, and passed the resolutions on the Journal, authorizing a Committee to confer anew with the Executive of the State, and, in case no satisfactory grounds should appear for expecting prompt and adequate exertions for suppressing the mutiny and supporting the public authority, authorizing the President, with the advice of the Committee, to summon the members to meet at Trenton or Princeton, in New Jersey.
The conference with the Executive produced nothing but a repetition of doubts concerning the disposition of the militia to act, unless some actual outrage were offered to persons or property.
It was even doubted whether a repetition of the insult to Congress would be a sufficient provocation.
During the deliberations of the Executive, and the suspense of the Committee, reports from the barracks were in constant vibration.
At one moment, the mutineers were penitent and preparing submissions; the next, they were meditating more violent measures.
Sometimes the bank was their object; then the seizure of the members of Congress, with whom they imagined an indemnity for their offence might be stipulated.
On Tuesday, about two o’clock, the efforts of the State authority being despaired of, and the reports from the barracks being unfavorable, the Committee advised the President to summon Congress to meet at Trenton, which he did verbally as to the members present, leaving behind him a General Proclamation for the press.
After the departure of Congress, the mutineers submitted, and most of them accepted furloughs under the resolution of Congress on that subject.
At the time of submission, they betrayed their leaders, the chief of whom proved to be a Mr. Carberry, a deranged officer, and a Mr. Sullivan, a lieutenant of horse; both of whom made their escape.
Some of the most active of the sergeants also ran off.
From the Journals of the Continental Congress, 1774-1789, Volume 24, their resolution:
Saturday, June 21, 1783
Resolved, That the president and supreme executive council of Pennsylvania, be informed that the authority of the United States having been this day grossly insulted by the disorderly and menacing appearance of a body of armed soldiers about the place within which Congress were assembled, and the peace of this city being endangered by the mutinous disposition of the said troops now in the barracks, it is, in the opinion of Congress, necessary that effectual measures be immediately taken for supporting the public authority.
Resolved, That the committee, on a letter from Colonel Butler, be directed to confer, without loss of time, with the supreme executive council of Pennsylvania, on the practicability of carrying the preceding resolution into effect: and that in case it shall appear to the committee that there is not a satisfactory ground for expecting adequate and prompt exertions of this State for supporting the dignity of the federal government, the President on the advice of the committee be authorized and directed to summon the members of Congress to meet on Thursday next at Trenton or Princeton, in New Jersey, in order that further and more effectual measures may be taken for suppressing the present revolt, and maintaining the dignity and authority of the United States.
Resolved, That the Secretary at War be directed to communicate to the Commander in Chief, the state and disposition of the said troops, in order that he may take immediate measures to dispatch to this city, such force as he may judge expedient for suppressing any disturbances that may ensue.*
* The entry for this day was made in the Journal by George Bond.
The Congress Commemorative Half Dollar Coin shows with an image of the Philadelphia State House, circa 1778.