The Main (German pronunciation: [ˈmaɪn] ^ⓘ) is the longest tributary of the Rhine. It rises as the White Main in the Fichtel Mountains of northeastern Bavaria^{[lower-alpha 1]} and flows west through central Germany for 525 kilometres (326 mi) to meet the Rhine below Rüsselsheim, Hesse. The cities of Mainz and Wiesbaden are close to the confluence.

The largest cities on the Main are Frankfurt am Main, Offenbach am Main and Würzburg.^[2] It is the longest river lying entirely in Germany (if the Weser-Werra are considered separate).

The Main flows through the north and north-west of the state of Bavaria then across southern Hesse; against the latter it demarcates a third state, Baden-Württemberg, east and west of Wertheim am Main, the northernmost town of that state.

The upper end of its basin opposes that of the Danube where the watershed is recognised by natural biologists, sea salinity studies (and hydrology science more broadly) as the European Watershed.

The Main begins near Kulmbach in Franconia at the joining of its two headstreams, the Red Main (Roter Main) and the White Main (Weißer Main). The Red Main originates in the Franconian Jura mountain range, 50 km (31 mi) in length, and runs through Creussen and Bayreuth. The White Main originates in the Fichtel Mountains; it is 41 km (25 mi) long. In its upper and middle section, the Main runs through the valleys of the German Highlands. Its lower section crosses the Lower Main Lowlands (Hanau-Seligenstadt Basin and northern Upper Rhine Plain) to Wiesbaden, where it discharges into the Rhine. Major tributaries of the Main are the Regnitz, the Franconian Saale, the Tauber, and the Nidda.^[3]

The name Main originates from Latin Moenis, Moenus or Menus. It is not related to the name of the city Mainz (Latin: Mogontiacum or Moguntiacum).

The Main is navigable for shipping from its mouth at the Rhine close to Mainz for 396 km (246 mi) to Bamberg. Since 1992, the Main has been connected to the Danube via the Rhine-Main-Danube Canal and the highly regulated Altmühl river. The Main has been canalized with 34 large locks (300 × 12 m or 984 × 39 ft) to allow CEMT class V vessels (110 × 11.45 m or 360.9 × 37.6 ft) to navigate the total length of the river. The 16 locks in the adjacent Rhine-Main-Danube Canal and the Danube itself are of the same dimensions.^{[citation needed]}

Tributaries from source to mouth:

• The Main in Frankfurt at night
• Main in Offenbach am Main
• Confluence into the Rhine at Mainz-Kostheim

Around Frankfurt are several large inland ports. Because the river is rather narrow on many of the upper reaches, navigation with larger vessels and push convoys requires great skill.

The largest cities along the Main are Frankfurt am Main, Offenbach am Main and Würzburg. The Main also passes the following towns: Burgkunstadt, Lichtenfels, Bad Staffelstein, Eltmann, Haßfurt, Schweinfurt, Volkach, Kitzingen, Marktbreit, Ochsenfurt, Karlstadt, Gemünden, Lohr, Marktheidenfeld, Wertheim, Miltenberg, Obernburg, Erlenbach/Main, Aschaffenburg, Seligenstadt, Hainburg, Hanau, Hattersheim, Flörsheim, and Rüsselsheim.

The river has gained enormous importance as a vital part of European "Corridor VII", the inland waterway link from the North Sea to the Black Sea.^[5]

In a historical and political sense, the Main line is referred to as the northern border of Southern Germany, with its predominantly Catholic population. The river roughly marked the southern border of the North German Federation, established in 1867 under Prussian leadership as the predecessor of the German Empire.

The river course also corresponds with the Speyer line isogloss between Central and Upper German dialects, sometimes mocked as Weißwurstäquator.^[6][7]

The Main-Radweg is a major German bicycle path alongside the river. Approximately 600 kilometres long (370 mi), it is the first long-distance instance awarded 5 stars by the General German Bicycle Club (ADFC) in 2008. It starts from Creußen or Bischofsgrün and ends in Mainz.^[8]

• Roman camp at Marktbreit

• Krassach (River)