The City of Harker Heights shall have power to maintain a City police force, prescribe the duties, powers and compensation of policemen and regulate their conduct; to appoint watchmen and prescribe their duties, powers and compensation; to suppress and prevent any riot, affray, disturbance or disorderly assembly within the city; to prevent, prohibit and suppress immoderate riding and driving in the streets; to police all parks, grounds, speedways, boulevards, cemeteries and all other property or places owned by the City and lying either within or without the City limits and used for municipal purposes.