Csengeri Piroska - Tóth Arnold (szerk.): A Herman Ottó Múzeum évkönyve 54. (Miskolc, 2015)

Régészet - Tóth Krisztina–Szabó Ádám–Homoki Balázs: Archaeological research at the Twin-barrows near Onga (Northeast Hungary in 2015)

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Krisztián Tóth—Ádám Szabó—Balázs Homoki

are slid along the track (KVAMME 2006a, 241). After de-staggering the map there are other noises that have to be taken care of so that subtle anomalies could be made visible. Such noises include point like magnetic anomalies and ploughs. To eliminate these spike-like extreme measurements — which may only be indicated by one measured point or one pixel at a raster picture we use Snuffler, which has a diverse and useful toolbar. Among them, there is a “de-spike” function and high cut — low pass filter. After finishing the processing with Snuffler, the measured data is ready to be interpreted, but regular lines — plough marks — are still visible on the map [Map 8. C).

The presence of plough marks on the anomaly map are the furrows and ridges that represent lesser and greater amounts of topsoil (KVAMME, 2006a, 238). It is possible to eliminate them due to their orientation and regularity using Fourier methods (KVAMME 2006a, 238). There are many free programs on the Internet which are suitable for the Fourier transformation, filtering and recovering transformed data. We would like to highlight a program for transformation called Gwyddion. This program was originally designed for SEM (scanning electron microscope) data processing. In order to make measured data appropriate for the program the anomaly map must be interpolated as a regular grid (KLAPETEK et. al. 2015, 37). The main goal was to eliminate plough marks — as it can be seen on the map it is not so disturbed. On the final filtered picture you can notice that the horizontal and vertical grooves are gone, but the contours of the anomalies remained (Map 8. D).

We fitted the anomaly map published by Tóth and others (TÓTH-PETHE-HATHÁZI 2014, 19, Fig. 4) to our anomaly map, from which we have digitized the circle ditches and most possible burials (Map 9. A—B). We identified 29 circular ditches in total, which currently seems to be placed in three groups; furthermore we digitized the ditch of the northwestern mound. Thus together with the two barrows — assuming that the second one also has a similar ditch — we documented 31 burials with circular ditches, however anomalies located between them suggest the existence of other graves without ditches. We can find the entrance of these fosses in the south in most cases like at the big barrow. The diameters of the circular ditches in the northern group are between 9 and 16 meters. The largest one has two fosses and the diameter of the outer one is 17 meters. We only know about one grave to the west of the northern barrow at this moment and only a part of it belongs to the surveyed area, but its diameter is

around 25 meters. In the eastern group the graves are located in a row and they are similar to each other in their size, the diameters of their ditches are between 9 and 10 meters. Based on the survey in the north line of the eastern group several fosses could have been dug into each other. On the south of this eastern group we can detect two bigger fosses, but with their 11 and

11.5 meter diameters they are not substantially different from the rest.

THE EXCAVATION

We carried out the excavation north from the northern barrow on the geomagnetically surveyed area between the 10th and 18th of August, 2015. The assumed burials were on the southwest part of this area; due to the new survey we knew their exact positioning. We selected the northernmost and smallest circular ditch with 9 meters in diameter (Map 10. A).

We marked out a 10 meters long and 1 m wide searching trench (Trench I) with RTK GPS, which intersected the anomalies of the circular ditch and the central one. We had to work with pickaxes because of the low humidity of the loamy humus (SI). We could register the loamy subsoil at 35 cm deep, in which the grey-brown spots of the circular ditch (S2) in both north and south end of the trench and another one (S3) in the middle have been detected. We found more recent ceramic fragments in the humus, while some prehistoric sherds (Fig. 1. 1—2) came to light at the southern part of the ditch. After cleaning the trench we created orthophotos with a Nikon lv3 camera to document the spots (Map 10. B). During the excavation of the circular ditch we found more black pottery fragments in the infilling, but their locations did not show any regularity. In the northern part of the ditch we found a red wheel made pottery fragment along a prehistoric sherd (Fig. 1. 3), and on the bottom of this part of the foss burnt bones were also revealed. The walls and bottom of the ditch were steep and curved, 100—110 cm wide and 70 cm deep from the top of the humus (Map 10. C). During the excavation of the spot in the middle, we also found burnt bone fragments. The depth of this (S3) was 10 cm from the cleaned surface, where we encountered the yellow, loamy subsoil. Its wall was splay and its bottom was flat in Trench I.

Because the middle spot (S3) clearly went out the trench, we opened another one (Trench II) to the west from the first one. It was 2 meters long and 2.5 meters wide. We also managed to register this patch in here and then documented using orthophotos. It did not deepen more than Trench I, just at its northern part,