When the same is accomplished in a campaign of seven weeks as was formerly done in a war of seven years, it is not necessary that fortified places should hold out a very long time.

A place that can sustain a siege of a month is now deemed sufficiently strong for ordinary campaigns; for by the end of that time the defensive army will either be destroyed, or be able to come to its succor.

In either case a longer defence would not be required.
A reference to the most important sieges of the last century or two will show that forts are, on an average, capable of sustaining a siege for more than that length of time.

Lille, in 1708, held the allies in check for a whole year; and again, in 1792, compelled the Austrians to raise the siege after an unsuccessful attack of fifteen days.
Antwerp, in 1585, sustained a siege of fourteen months against greatly superior forces; in 1814 Carnot defended the citadel of this place for four months, and until an armistice had been concluded between the contending parties; in 1832, it sustained, with a garrison of only 4,500 men and 145 pieces of ordnance, a siege of twenty-five days, against a force of 55,000 men and 223 cannon.
Namur, near the end of the seventeenth century, sustained a siege of ten weeks.
Ismail, in 1790, sustained a siege of more than two months against the Russians.
Maestricht, in 1793, sustained a siege of nearly two weeks; and again, in 1794, sustained a blockade and siege of nearly two months.
Magdeburg, in the thirty years' war, resisted the army of Wallenstein for seven months; and in 1813-14, although garrisoned by only 4,000 men, it for a long time resisted the overwhelming forces of the allies.
Dantzic, at the same time, sustained a siege against superior forces for more than nine months.
Landau, in 1793, sustained a siege of nine months.
Valenciennes and Mayence, in 1793, each sustained a siege of about three months.
Charleroi, Fort Vauban, and L'Ecluse, in 1794, each sustained a siege of about thirty days.
Quesnoy, in 1794, sustained a siege of about three weeks.
Rosas, in 1795, sustained a siege of some seventy days.
Mantua, in 1796-7, protected from invasion, for eight months, the Tyrol and the heart of the Austrian monarchy.
Kehl and Huninguen, in 1796, sheltered Moreau for three months against all the efforts of the Archduke Charles.
St.Jean d'Acre, in 1799, sustained a siege of sixty days of open trench.
Ulm, in 1800, held Moreau in check for more than a month.
Genoa, in 1800, sustained a blockade of sixty and a siege of forty days.
Saragossa in 1808 sustained a close siege of near two months; and in 1809 it was again besieged for two months.
Rosas in 1808 sustained a siege of thirty days.
Gerona in 1809 sustained a siege and blockade of seven months, nearly four of them being of open trench.
Mequinenza (a very small work) in 1810 sustained a siege of more than two weeks.
Astorga in 1810 sustained a siege of thirty days; twenty-four being of open trench.
Lerida in 1810 sustained a siege of thirty days, two weeks being of open trench.
Ciudad Rodrigo in 1810 sustained a siege of two months.
Almeida in 1810 sustained a siege of more than a month.
Tortosa in 1810 sustained a siege of six months.
Tarragona in 1811 sustained a siege of nearly two months.
Badajos in 1811 sustained a siege of more than forty days open trench.
Lerida in 1811 sustained a siege of two weeks open trench.
Saguntum in 1811 sustained a siege of a month.
Valencia in 1811-12 sustained a siege of two months Ciudad Rodrigo in 1812 sustained a blockade of several months, and a close siege of two weeks.
Badajos in 1812 sustained twenty-one days of open trenches.
Burgos in 1812 sustained thirty-three days of open trenches.
St.Sebastian in 1813 sustained a siege and blockade of nearly three months, with fifty-nine days of open trenches.
Pampeluna in 1813 sustained a siege of more than four months.
Monzon in 1813-14 also sustained a siege of more than four months.
This list might be increased with numerous other examples, to show that even poorly fortified towns are capable of defending themselves, on an average, for more than a month.

These examples, be it remembered, are nearly all taken from a period of history since any material improvements have been made in the art of attack.