Alfred showed a wise precaution against future assaults in constructing
fortresses at the most important points within his control. Before his
day the Saxons had but few fortified positions, and this want of forts
had greatly facilitated the Danish conquest. But the Danes, as soon as
they gained a strong position, fortified it, and were never afterwards
ejected by force. Probably Alfred took the hint from them. He rebuilt
and strengthened the fortresses along the coast, as he had four precious
years of unmolested work; and for this his small kingdom was doubtless
severely taxed. He imported skilled workmen, and adopted the newest
improvements. He made use of stone instead of timber, and extended his
works of construction to palaces, halls, and churches, as well as
castles. So well built were his fortifications, that no strong place was
ever afterwards wrested from him. In those times the defence of kingdoms
was in castles. They marked the feudal ages equally with monasteries and
cathedral churches. Castles protected the realm from invasion and
conquest, as much as they did the family of a feudal noble. The wisdom
as well as the necessity of fortified cities was seen in a marked manner
when the Northmen, in 885, stole up the Thames and Medway and made an
unexpected assault on Rochester. They were completely foiled, and were
obliged to retreat to their ships, leaving behind them even the spoil
they had brought from France. This successful resistance was a great
moral assistance to Alfred, since it opened the eyes of bishops and
nobles to the necessity of fortifying their towns, to which they had
hitherto been opposed, being unwilling to incur the expense. So it was
not long before Alfred had a complete chain of defences on the coast, as
well as around his cities and palaces, able to resist sudden
attacks,--which he had most to fear. His great work of fortification was
that of London, which, though belonging to him by the peace of Wedmore,
was neglected, fallen to decay, filled with lawless bands of marauders
and pirates, and defenceless against attack. In 886 he marched against