Originally inhabited by the Helvetians, or Helvetic Celts, the territory comprising modern Switzerland was conquered by Julius Caesar during the Gallic wars and made part of the Roman Empire. It remained a Roman province until the 4th century AD. Under Roman influence, the population reached a high level of civilization and enjoyed a flourishing commerce. Important cities, such as Geneva, Basel, and Zurich, were linked by military roads that also served as trade arteries between Rome and the northern tribes.
After the decline of the Roman Empire, Switzerland was invaded by Germanic tribes from the north and west. Some tribes, such as the Alemanni in central and northeastern Switzerland, and the Burgundians, who ruled western Switzerland, settled there. In 800, the country became part of Charlemagne's empire. It later passed under the dominion of the German emperors in the form of small ecclesiastic and temporal holdings subject to imperial sovereignty.
In 1291, representatives of the three forest cantons of Uri, Schwyz, and Unterwalden signed the Eternal Alliance. This united them in the struggle against "foreign" rule by the Hapsburgs, who then held the German imperial throne. At the battle of Morganten in 1315, the Swiss defeated the Hapsburg army and secured quasi-independence within the German Empire as the Swiss Confederation.
Under the Treaty of Westphalia in 1648, European countries recognized Switzerland's independence from the Holy Roman Empire and its neutrality.
In 1798, armies of the French Revolution conquered Switzerland. The Treaty of Vienna and the Second Peace of Paris in 1815 re-established Swiss independence, and the powers participating in the Congress of Vienna agreed to recognize Swiss permanent neutrality.
Switzerland adopted a federal constitution in 1848, modeled in part on the U.S. Constitution. The Swiss amended their constitution extensively in 1874, establishing federal responsibility for defense, trade, and legal matters. Since then, continued political, economic, and social improvement has characterized Swiss history. The Swiss did not participate in either world war.