THE POLANIAN DYNASTY 67
introduced on the monetary scale: 48 grosze (grossi) = 24 skojca (sesterce) = 4
wiardunki (farthings) = 1 grzywna (mark)= 197 grams of silver. External trade
increased too. The overland trade on the east-west route between Germany and
the Black Sea thrived on the exchange of furs, honey, cattle, and slaves, for tex-
tiles and implements. In the thirteenth century contacts were established with
the Mongol Empire. Cracow also lay on the north-south route from the Baltic
to the Balkans. On this ancient 'amber road' in the Middle Ages, Hungarian
copper moved north, whilst cloth and salted herrings moved south. The activi-
ties of the Hansa, to which both Cracow and Wroclaw belonged, affected the
interior of Poland no less than the ports of Pomerania and Prussia.
War was the natural condition of medieval society. Apart from the incessant
civil wars for control of the monarchy or of the principalities, armed conflict
with foreign foe was the order of the day. In the early period, organized raiding
constituted an important sector of the primitive economy - loot, slaves, and
food stores being an essential supplement to the products of subsistence farm-
ing. On the Prussian and Lithuanian frontiers, it continued as the normal way
of life until the end of the fourteenth century, and for the Tartars of the
south-east, well into modern times. Increasingly, however, wars were fought
for the delineation of frontiers, and for the permanent control of territory. At
first, the area of prime concern lay to the west, with the relentless expansion of
German settlement into the imperial marches of Brandenburg, Lusatia, and
Meissen, and with disputes over Pomerania, Silesia, and Bohemia. Later, it
shifted to the east and to the north - to Ruthenia, and above all to Prussia. Piast
Poland's one natural barrier stood in the south, where the Carpathian moun-
tains acted as a lofty, pristine screen.
To sustain constant warfare, a complex military organization was required.
In the era of Mieszko I and Boleslaw Chrobry great importance was laid on the
royal grod or fortress, garrisoned by a detachment of the guard, and fortified
with earthworks, palisades, and moats. Several such garrisons are known - at
Gniezno, Poznan, Gdecz, and 'Wladislavia', each with several thousand men. In
view of the vast terrain, it was impossible to deny the enemy access to one's
home territory. To attack, one needed only to exploit the element of surprise.
Defensive tactics depended largely on channelling the line of the enemy's
advance by protective screens - river patrols and flooded valleys - and on hold-
ing the fortresses with their reserves of food and concentrations of men. The
tribal host must have called on almost every able-bodied man. From the twelfth
century onwards, however, peasants were gradually exempted from regular
service, except when defending their own locality, and were put to work to
support the rising costs of their knightly master's equipment and training. The
proportion of mounted cavalry in the host grew as the number of spearmen and
bowmen declined. The towns provided their own defence. The reunification of
the country after 1320 permitted the mobilization of much larger forces. Under
Casimir the Great, all landholders were legally required to present themselves
for war, complete with arms, armour, horses, and retinue. The pospolite