Rabbinic sources describe the Temple menorah as hammered from a single ingot of gold rather than assembled from separately cast branches, a construction method called miksha that later commentators debated as either a strict requirement or an ideal rarely achieved in practice.
How it was made, and how reproductions are made now
A one piece hammered lampstand of that size and weight is an exceptionally demanding goldsmith's task, which is likely why later replicas and ceremonial menorahs, including the large one displayed near the Knesset, are cast or built from separately joined sections rather than hammered whole. Modern synagogue and decorative menorahs are typically brass or silver, cast in a foundry rather than hand forged, since the original one piece requirement applied specifically to the Temple vessel rather than to every representation of it.
Not to be confused with the Hanukkah lamp
The seven branched menorah is frequently and incorrectly conflated with the nine branched Hanukkah lamp, properly called a hanukkiah, which commemorates a different event entirely and was never part of Temple service. Since the Temple no longer stands, no menorah today is lit as the original was, a menorah now functions as a national and religious emblem, most visibly on the State of Israel's coat of arms, or as a synagogue ornament rather than as a working lamp filled with oil.